test-wireproto: move from dict() construction to {} literals

The latter are both faster and more consistent across Python 2 and 3.

tests/test-wireproto.py

@@ -18,7 +18,7 b' class clientpeer(wireproto.wirepeer):'
     @wireproto.batchable
     def greet(self, name):
         f = wireproto.future()
-        yield wireproto.todict(name=mangle(name)), f
+        yield {'name': mangle(name)}, f
         yield unmangle(f.value)
 
 class serverrepo(object):