[PR] Fix typo in installation instructions
[PR] Fix typo in installation instructions

Summary:
Installation instructions for babel + NPM instructed installing the incorrect babel plugin.
Pull Request resolved: https://github.com/facebook/flow/pull/7933

Reviewed By: gabelevi

Differential Revision: D16339722

Pulled By: mroch

fbshipit-source-id: e176cea24f48ef6507e267a5bf88a883b32daee0

nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow