Fix regexp for --update-tests/--update-unexpected.

As it was written, it ensured that the place where the old expected output
starts doesn't also start with !!end, which isn't exactly what it meant
to do.

Change-Id: I001b23c549c6adc427f7a74efd9eec5c83a3130c
Merge "Fix regexp for --update-tests/--update-unexpected."