tests: use absolulte_import in test-wireproto.py

tests/test-check-py3-compat.t

@@ -219,7 +219,6 b''
   tests/test-url.py not using absolute_import
   tests/test-url.py requires print_function
   tests/test-walkrepo.py requires print_function
-  tests/test-wireproto.py not using absolute_import
   tests/test-wireproto.py requires print_function
   tests/tinyproxy.py not using absolute_import
   tests/tinyproxy.py requires print_function

tests/test-wireproto.py

@@ -1,3 +1,5 b''
+from __future__ import absolute_import
+
 from mercurial import wireproto
 
 class proto(object):