Summary:
Update clang-format script to format diff since last commit from master,
instead of just last commit. In our common workflow we usually endup
with multiple commits for a single PR. This change make it easier to
format all stacking changes.
Closes https://github.com/facebook/rocksdb/pull/1684
Differential Revision: D4340597
Pulled By: yiwu-arbug
fbshipit-source-id: c18949e
fc0c6fd984