Make the negative test more specific.

Summary:
Make the negative test more specific.
Otherwise it can accidentally match injected code.

Reviewers: aaron.ballman

CC: klimek, cfe-commits, revane

Differential Revision: http://llvm-reviews.chandlerc.com/D2257

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@195512 91177308-0d34-0410-b5e6-96231b3b80d8