Update release notes (check SVN commit-after-approval access)

Summary:
I was just granted commit-after-approval access to SVN,
and @clattner recommended I try a test commit.

So, this tweaks the release notes as a test.

Reviewers: hokein, alexfh

Reviewed By: hokein

Subscribers: Wizard

Differential Revision: https://reviews.llvm.org/D39559

llvm-svn: 317261