Fixed - updated_at timestamp reflects recent actions (#412)

Looks good. I tested it and it seems to update the timestamp correctly when interacting with the API. I am curious if there are any other cases when we should be updating the timestamp.

graphspace/mixins.py

@@ -17,4 +17,4 @@ class IDMixin(object):
 
 class TimeStampMixin(object):
 	created_at = Column(TIMESTAMP, server_default=func.now(), nullable=False)
-	updated_at = Column(TIMESTAMP, server_default=func.now(), nullable=False)
+	updated_at = Column(TIMESTAMP, server_default=func.now(), nullable=False, onupdate=func.now())