fix(default dim): correctly defines the default dim as string cause a…

… selection has to be string since odoo 13

base_geoengine/fields.py

@@ -30,7 +30,7 @@ class GeoField(fields.Field):
     """
 
     geo_type = None
-    dim = 2
+    dim = "2"
     srid = 3857
     gist_index = True