Merge pull request #957 from DomT4/xcode_8_stable

xcode: 8.0 is no longer prerelease

Library/Homebrew/os/mac/xcode.rb

@@ -28,8 +28,8 @@ module OS
       end
 
       def prerelease?
-        # TODO: bump to version >= "8.1" after Xcode 8.0 is stable.
-        version > "7.3.1"
+        # TODO: bump to version >= "8.2" after Xcode 8.1 is stable.
+        version >= "8.1"
       end
 
       def outdated?