docs: Fix inconsistent titles.

Sphinx was whining about this.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@171796 91177308-0d34-0410-b5e6-96231b3b80d8

docs/ClangTools.rst

@@ -71,7 +71,7 @@ tools that very specifically compliment, and allow use and testing of
 *Clang* specific functionality.
 
 ``clang-check``
-~~~~~~~~~~~~~~~
+---------------
 
 This tool combines the LibTooling framework for running a Clang tool
 with the basic Clang diagnostics by syntax checking specific files in a