Updated browser icons in README (#2238)
Updated browser icons in README (#2238)

Summary:
**Summary**

Updated README to show current browser icons in compatibility table
Pull Request resolved: https://github.com/facebook/draft-js/pull/2238

Reviewed By: elboman

Differential Revision: D18226486

Pulled By: mrkev

fbshipit-source-id: 3aed87817e9a0a9ea0b08809420b04e7411df3f2

facebook/draft-js