add missing `

Author: kmike

NEWS

@@ -24,7 +24,7 @@ Deprecation removals (#169):
 The following functions are deprecated, and will be removed in future releases
 (#170):
 
-- `w3lib.util.str_to_unicode``
+- ``w3lib.util.str_to_unicode``
 - ``w3lib.util.unicode_to_str``
 - ``w3lib.util.to_native_str``