Fix typo it's -> its

Author: the-vishal

elasticsearch/connection_pool.py

@@ -29,7 +29,7 @@ class ConnectionSelector(object):
 
     Example of where this would be useful is a zone-aware selector that would
     only select connections from it's own zones and only fall back to other
-    connections where there would be none in it's zones.
+    connections where there would be none in its zones.
     """
 
     def __init__(self, opts):