Fix Now function to return the statement time rather than transaction time

Author: timgraham

django_cockroachdb/functions.py

@@ -6,7 +6,7 @@
 from django.db.models.expressions import When
 from django.db.models.functions import (
     ACos, ASin, ATan, ATan2, Cast, Ceil, Coalesce, Collate, Cos, Cot, Degrees,
-    Exp, Floor, JSONArray, JSONObject, Ln, Log, Radians, Round, Sin, Sqrt,
+    Exp, Floor, JSONArray, JSONObject, Ln, Log, Now, Radians, Round, Sin, Sqrt,
     StrIndex, Tan,
 )
 
@@ -79,6 +79,7 @@ def register_functions():
     Collate.as_cockroachdb = collate
     JSONArray.as_cockroachdb = JSONArray.as_postgresql
     JSONObject.as_cockroachdb = JSONObject.as_postgresql
+    Now.as_cockroachdb = Now.as_postgresql
     Round.as_cockroachdb = round_cast
     StrIndex.as_cockroachdb = StrIndex.as_postgresql
     When.as_cockroachdb = when