Update toolchain versions in README.md

Author: MaxDesiatov

README.md

@@ -13,9 +13,9 @@ The toolchains can be installed via [`swiftenv`](https://github.com/kylef/swifte
 e.g.
 ```sh
 
-$ swiftenv install https://github.com/swiftwasm/swift/releases/download/swift-wasm-DEVELOPMENT-SNAPSHOT-2020-03-08-a/swift-wasm-DEVELOPMENT-SNAPSHOT-2020-03-08-a-osx.tar.gz
+$ swiftenv install https://github.com/swiftwasm/swift/releases/download/swift-wasm-DEVELOPMENT-SNAPSHOT-2020-04-27-a/swift-wasm-DEVELOPMENT-SNAPSHOT-2020-04-27-a-osx.tar.gz
 $ swift --version
-Swift version 5.2-dev (LLVM 7fc8796bc1, Swift 5be35e7aee)
+Swift version 5.3-dev (LLVM 7fc8796bc1, Swift 5be35e7aee)
 Target: x86_64-apple-darwin19.3.0
 ```