chore: Update Xcode version in README (#723)

Author: palpatim

README.md

@@ -39,7 +39,7 @@ This library is licensed under the Apache 2.0 License.
 
 ## Installation
 
-Amplify requires Xcode 11 or higher to build.
+Amplify requires Xcode 11.4 or higher to build.
 
 ### CocoaPods