Use JSON canonical form for Dict value

It allows to make equality comparison.

issue7013
review39041002

CHANGELOG

@@ -1,3 +1,4 @@
+* Use JSON canonical form for Dict value
 * Remove rules on user
 * Add monetary formatting to language
 * Add exceptional parent language

trytond/model/fields/dict.py

@@ -37,7 +37,9 @@ class Dict(Field):
         if value is None:
             return None
         assert isinstance(value, dict)
-        return json.dumps(value, cls=JSONEncoder, separators=(',', ':'))
+        # Use canonical form
+        return json.dumps(
+            value, cls=JSONEncoder, separators=(',', ':'), sort_keys=True)
 
     def translated(self, name=None, type_='values'):
         "Return a descriptor for the translated value of the field"