Summary:
We missed updating version.h on master when cutting 5.11.fb and 5.12.fb branches. It should be the same as the version in the latest release branch (or should it be one more?).

I noticed this when trying to run some upgrade/downgrade tests from 5.11 to some new code on master.
Closes https://github.com/facebook/rocksdb/pull/3611

Differential Revision: D7282917

Pulled By: sagar0

fbshipit-source-id: 205ee75b77c5b6bbcea95a272760b427025a4aba