Summary:
cli / packager was broken on Windows after 28f1c67ced.
Babel `only` regexp option requires paths to use forward slashes only but `__dirname` will use backslashes on windows. This simply adds a replace to normalize to forward slashes.
cc jeanlauliac cpojer
Closes https://github.com/facebook/react-native/pull/11850
Reviewed By: cpojer
Differential Revision: D4409143
Pulled By: jeanlauliac
fbshipit-source-id: a705236630959f762e53100299ab073ec9a29ee1