releasenotes: fix a version nbr

git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_60@323948 91177308-0d34-0410-b5e6-96231b3b80d8

Author: zmodem

docs/ReleaseNotes.rst

@@ -15,7 +15,7 @@ Introduction
 ============
 
 This document contains the release notes for the LLVM Compiler Infrastructure,
-release 5.0.0.  Here we describe the status of LLVM, including major improvements
+release 6.0.0.  Here we describe the status of LLVM, including major improvements
 from the previous release, improvements in various subprojects of LLVM, and
 some of the current users of the code.  All LLVM releases may be downloaded
 from the `LLVM releases web site <http://llvm.org/releases/>`_.