Summary:
Adjusted history for 6.6.1 and 6.6.2, switched master version to 6.7.0.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6320

Differential Revision: D19499272

Pulled By: gfosco

fbshipit-source-id: 2bafb2456951f231e411e9c03aaa4c044f497684