[Doc] fix second error in UsersManual

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@344388 91177308-0d34-0410-b5e6-96231b3b80d8

docs/UsersManual.rst

@@ -1844,7 +1844,7 @@ For example, to specify that ``absl::string_view`` and ``std::string_view``
 should be treated as equivalent when matching profile data, the following
 remapping file could be used:
 
-.. code-block::
+.. code-block:: text
 
   # absl::string_view is considered equivalent to std::string_view
   type N4absl11string_viewE St17basic_string_viewIcSt11char_traitsIcEE