[clang-tidy] correct clang-tidy-diff.py help message
[clang-tidy] correct clang-tidy-diff.py help message

Summary:
Looks like the original code was copied from clang-format-diff.py.
Update help message to make it clang-tidy specific.

Reviewers: klimek, alexfh

Subscribers: Eugene.Zelenko, cfe-commits

Patch by Igor Sugak!

Differential Revision: http://reviews.llvm.org/D21050


git-svn-id: a34e9779ed74578ad5922b3306b3d80a0c825546@272144 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra