trivial: put back return at end of 3.4-compatibility

Author: kay-kim

source/release-notes/3.4-compatibility.txt

@@ -153,4 +153,4 @@ Driver Compatibility Changes
 
 To use the various new features such as the new :ref:`3.4-decimal` and
 :ref:`collation` with a MongoDB driver, an upgrade to a driver version
-that supports these features is necessary.
+that supports these features is necessary.