Fix bug with handoff get_capabilities as json

Author: swainn

tethys_apps/base/handoff.py

@@ -65,7 +65,7 @@ def get_capabilities(self, app_name=None, external_only=False, jsonify=False):
                 handlers = [handler for handler in handlers if not handler.internal]
 
             if jsonify:
-                handlers = json.dumps([handler.__dict__ for handler in handlers])
+                handlers = json.dumps([handler.__dict__() for handler in handlers])
 
             return handlers