Update the Xcode version to 11.3

Author: shahmishal

README.md

@@ -86,7 +86,7 @@ Please make sure you use Python 2.x. Python 3.x is not supported currently.
 
 #### macOS
 
-To build for macOS, you need [Xcode 11.2](https://developer.apple.com/xcode/downloads/).
+To build for macOS, you need [Xcode 11.3](https://developer.apple.com/xcode/downloads/).
 The required version of Xcode changes frequently, and is often a beta release.
 Check this document or the host information on <https://ci.swift.org> for the
 current required version.