Fix sphinx warning from r299470

llvm-svn: 299481
diff --git a/clang/docs/LanguageExtensions.rst b/clang/docs/LanguageExtensions.rst
index fc8780a..6427067 100644
--- a/clang/docs/LanguageExtensions.rst
+++ b/clang/docs/LanguageExtensions.rst
@@ -2342,6 +2342,6 @@
   }
 
 
-The pragma can also be used with 'off' which turns FP contraction off for a
+The pragma can also be used with ``off`` which turns FP contraction off for a
 section of the code. This can be useful when fast contraction is otherwise
 enabled for the translation unit with the ``-ffp-contract=fast` flag.