ReleaseNotes: missing char

git-svn-id: https://llvm.org/svn/llvm-project/cfe/branches/release_39@279176 91177308-0d34-0410-b5e6-96231b3b80d8

docs/ReleaseNotes.rst

@@ -87,7 +87,7 @@ included by an ``#include <stdafx.h>`` in each source file instead of by a
 
 clang-cl has a new flag, ``/imsvc <dir>``, for adding a directory to the system
 include search path (where warnings are disabled by default) without having to
-set ``%INCLUDE``.
+set ``%INCLUDE%``.
 
 C Language Changes in Clang
 ---------------------------