lower mastodon.social default hits in known instances to 0

if the user uses mastodon.social, it will be raised to 1, if not then it
can be replaced by the third instance the user logs into

libforget/known_instances.py

@@ -30,7 +30,7 @@ class KnownInstances(object):
     def __default(self):
         self.instances = [{
                 "instance": "mastodon.social",
-                "hits": 5
+                "hits": 0
             }]
 
     def clear(self):

test/test_known_instances.py

@@ -5,7 +5,7 @@ def test_known_instances_defaults():
     ki = KnownInstances()
     assert len(ki.instances) == 1
     assert ki.instances[0]['instance'] == 'mastodon.social'
-    assert ki.instances[0]['hits'] > 0
+    assert isinstance(ki.instances[0]['hits'], int)
 
 
 def test_known_instances_clear():