Fix typo in commit 4b061a25b579c and 2c2176043b739.

It's IsolateService, not IsolateServer.

TBR=vadimsh@chromium.org
BUG=

Review URL: https://codereview.appspot.com/221200043
diff --git a/appengine/isolate/main_frontend.py b/appengine/isolate/main_frontend.py
index 26a852d..6603d44 100644
--- a/appengine/isolate/main_frontend.py
+++ b/appengine/isolate/main_frontend.py
@@ -30,7 +30,7 @@
   # App that serves HTML pages and old API.
   frontend = handlers_frontend.create_application(False)
   # App that serves new endpoints API.
-  api = endpoints.api_server([handlers_endpoints.IsolateServer])
+  api = endpoints.api_server([handlers_endpoints.IsolateService])
   return frontend, api