Update title of the ReleaseNodes doc.

It was still "3.5 (In-Progress)" - should be 3.6

llvm-svn: 219153
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 1c09a7b..daab804 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -1,5 +1,5 @@
 =====================================
-Clang 3.5 (In-Progress) Release Notes
+Clang 3.6 (In-Progress) Release Notes
 =====================================
 
 .. contents::