Add trailing period on "This reverts commit ..." line

When a commit is reverted with the Web UI, the generated commit
message includes the line "This reverts commit <sha1>" without a
trailing period.

However, if the same revert is done manually from the command line
with `git revert`, the generated commit message includes the line
"This reverts commit <sha1>." with a trailing period.

Update the message generated when reverting from the Web UI to
include the trailing period on the line.

Change-Id: Iacb09a25bce2335ea65ad46d2676828cb402eb1d
2 files changed