Fix reStructuredText warning.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@313320 91177308-0d34-0410-b5e6-96231b3b80d8

Author: DougGregor

docs/Modules.rst

@@ -669,7 +669,7 @@ Note that, if ``Derived.h`` includes ``Base.h``, one can simply use a wildcard e
   all of them).
 
 Re-export Declaration
-~~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~~~~~~
 An *export-as-declaration* specifies that the current module will have
 its interface re-exported by the named module.