c++11 status: Replace references to "SVN" with "3.1" to avoid confusion when they diverge.

Color is still yellow, as 3.1 isn't released yet.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@155217 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed