Updated link in LanguageExtensions.rst to point to BlockLanguageSpec.rst instead of BlockLanguageSpec.txt.

Thanks to Jean-Daniel Dupas for comments!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@170644 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed