Use "Contributed by ..." style in whatsnew/3.7.rst (python#339)

Author: berkerpeksag

Doc/whatsnew/3.7.rst

@@ -84,7 +84,8 @@ Other Language Changes
   (Contributed by Robert Xiao in :issue:`28927`.)
 
 * :exc:`ImportError` now displays module name and module ``__file__`` path when
-  ``from ... import ...`` fails. :issue:`29546`.
+  ``from ... import ...`` fails.
+  (Contributed by Matthias Bussonnier in :issue:`29546`.)
 
 
 New Modules