Bug 1381876 - Make client.Session#maximize a method. r=automatedtester

The Maximize Window command is a POST endpoint and should consequently
be a method, not a property.

MozReview-Commit-ID: DJfKdhMIX75

--HG--
extra : rebase_source : 03409f3a30ac338704921801832d3210e8ef9236

testing/web-platform/tests/tools/webdriver/webdriver/client.py

@@ -263,7 +263,6 @@ class Window(object):
         body = {"x": x, "y": y}
         self.session.send_session_command("POST", "window/rect", body)
 
-    @property
     @command
     def maximize(self):
         return self.session.send_session_command("POST", "window/maximize")