typo fix (facebook#4134)

Author: fejes713

CONTRIBUTING.md

@@ -11,27 +11,27 @@ Following these guidelines helps to communicate that you respect the time of the
 As much as possible, we try to avoid adding configuration and flags. The purpose of this tool is to provide the best experience for people getting started with React, and this will always be our first priority. This means that sometimes we [sacrifice additional functionality](https://gettingreal.37signals.com/ch05_Half_Not_Half_Assed.php) (such as server rendering) because it is too hard to solve it in a way that wouldn’t require any configuration.
 
 We prefer **convention, heuristics, or interactivity** over configuration.<br>
-Here’s a few examples of them in action.
+Here are a few examples of them in action.
 
 ### Convention
 
 Instead of letting the user specify the entry filename, we always assume it to be `src/index.js`. Rather than letting the user specify the output bundle name, we generate it, but make sure to include the content hash in it. Whenever possible, we want to leverage convention to make good choices for the user, especially in cases where it’s easy to misconfigure something.
 
 ### Heuristics
 
-Normally, `npm start` runs on port `3000`, and this is not explicitly configurable. However some environments like cloud IDEs want the programs to run on a specific port to serve their output. We want to play well with different environments, so Create React App reads `PORT` environment variable and prefers it when it is specified. The trick is that we know cloud IDEs already specify it automatically so there is no need for the user to do anything. Create React App relies on heuristics to do the right thing depending on environment.
+Normally, `npm start` runs on port `3000`, and this is not explicitly configurable. However, some environments like cloud IDEs want the programs to run on a specific port to serve their output. We want to play well with different environments, so Create React App reads `PORT` environment variable and prefers it when it is specified. The trick is that we know cloud IDEs already specify it automatically, so there is no need for the user to do anything. Create React App relies on heuristics to do the right thing depending on environment.
 
-Another example of this is how `npm test` normally launches the watcher, but if the `CI` environment variable is set, it will run tests once. We know that popular CI environments set this variable so the user doesn’t need to do anything. It just works.
+Another example of this is how `npm test` normally launches the watcher, but if the `CI` environment variable is set, it will run tests once. We know that popular CI environments set this variable, so the user doesn’t need to do anything. It just works.
 
 ### Interactivity
 
-We prefer to add interactivity to the command line interface rather than add configuration flags. For example, `npm start` will attempt to run with port `3000` by default but it may be busy. Many other tools just fail in this case and ask that you pass a different port, but Create React App will display a prompt asking if you’d like to run the app on the next available port.
+We prefer to add interactivity to the command line interface rather than add configuration flags. For example, `npm start` will attempt to run with port `3000` by default, but it may be busy. Many other tools just fail in this case and ask that you pass a different port, but Create React App will display a prompt asking if you’d like to run the app on the next available port.
 
 Another example of interactivity is `npm test` watcher interface. Instead of asking people to pass command line flags for switching between test runner modes or search patterns, we print a hint with keys that you can press during the test session to instruct watcher what to do. Jest supports both flags and interactive CLI but Create React App prefers long-running sessions to keep user immersed in the flow over short-running sessions with different flags.
 
 ### Breaking the Rules
 
-No rules are perfect. Sometimes we may introduce flags or configuration if we believe the value is high enough to justify the mental cost. For example, we know that apps may be hosted paths different from the root, and we need to support this use case. However we still try to fall back to heuristics when possible. In this example, we ask that you specify `homepage` in `package.json`, and infer the correct path based on it. We also nudge the user to fill out the `homepage` after the build so the user becomes aware that the feature exists.
+No rules are perfect. Sometimes we may introduce flags or configuration if we believe the value is high enough to justify the mental cost. For example, we know that apps may be hosted paths different from the root, and we need to support this use case. However, we still try to fall back to heuristics when possible. In this example, we ask that you specify `homepage` in `package.json`, and infer the correct path based on it. We also nudge the user to fill out the `homepage` after the build, so the user becomes aware that the feature exists.
 
 ## Submitting a Pull Request
 
@@ -96,7 +96,7 @@ More detailed information are in the dedicated [README](/packages/react-scripts/
 
 ## Tips for contributors using Windows
 
-The scripts in tasks folder and other scripts in `package.json` will not work in Windows out of the box. However, using [Bash on  windows](https://msdn.microsoft.com/en-us/commandline/wsl/about) makes it easier to use those scripts without any workarounds. The steps to do so are detailed below: 
+The scripts in tasks folder and other scripts in `package.json` will not work in Windows out of the box. However, using [Bash on  windows](https://msdn.microsoft.com/en-us/commandline/wsl/about) makes it easier to use those scripts without any workarounds. The steps to do so are detailed below:
 
 ### Install Bash on Ubuntu on Windows