Fix formatting in sqlalchemy_utils.observer around the observer object.

Make instantiation of the default observer object separated by two spaces
from PropertyObserver class declaration, instead of one.

sqlalchemy_utils/observer.py

@@ -317,6 +317,7 @@ class PropertyObserver(object):
             for callback, objs in callback_objs.items():
                 callback(root_obj, *[objs[i] for i in range(len(objs))])
 
+
 observer = PropertyObserver()