Revert ReleaseNotes.rst

Author: yicuixi

clang/docs/ReleaseNotes.rst

@@ -634,4 +634,4 @@ tree.
 
 If you have any questions or comments about Clang, please feel free to
 contact us on the `Discourse forums (Clang Frontend category)
-<https://discourse.llvm.org/c/clang/6>`_.
+<https://discourse.llvm.org/c/clang/6>`_.