docs: fix the spell error (PlasmoHQ#118)

Author: MonsterPi13

src/pages/framework/workflows/dev.mdx

@@ -59,7 +59,7 @@ This is useful when you have dependencies that don't play well with source maps.
 The development server will, by default, bind to `localhost` and port `1012`. You can change these with `--serve-host` and `--serve-port`:
 
 ```sh
-plasmo dev --serve-host=localhost --serve-port-1012
+plasmo dev --serve-host=localhost --serve-port=1012
 ```
 
 Similarly, the hot module reload websocket will, by default, bind to `localhost` and port `1815`, with the build reporter binding to the HMR socket + 1 (1816 by default). You can change these with `--hmr-host` and `--hmr-port`: