Fixed the version number, since this is no longer a release candidate.

Change-Id: Ia0c6e9f5dd40e048636614fc1fd1909b32ef80cc
Merge "Fixed the version number, since this is no longer a release candidate." into REL1_21
bump ver to 1.21.1

Change-Id: Ic4178113f6325e6608e8b70d1d54bd5ef77f0c59
update release notes

Change-Id: Ib7d01f56a48bcba496505bece850e266c3704e18
Typo fixes in RELEASE-NOTES-1.21

- Changed 'an' to 'a'
- Added a comma

Change-Id: I11b5f68b46592f98089e2f6a2e61323f20c1fe05
Merge branch 'REL1_21' of https://gerrit.wikimedia.org/r/p/mediawiki/core into REL1_21