Remove statement that TweetStream is not 2.0.0-compatible

This has been fixed since the 2.6.0 release, see:
https://github.com/tweetstream/tweetstream/blob/master/CHANGELOG.md#version-260
Merge pull request #553 from mrgilman/remove-inaccurate-documentation-re-tweetstream

Remove statement that TweetStream is not 2.0.0-compatible