docs: fix simple typo, underyling -> underlying (#254)

There is a small typo in happybase/connection.py.

Should read `underlying` rather than `underyling`.

Author: timgates42

happybase/connection.py

@@ -176,7 +176,7 @@ def open(self):
         self.transport.open()
 
     def close(self):
-        """Close the underyling transport to the HBase instance.
+        """Close the underlying transport to the HBase instance.
 
         This method closes the underlying Thrift transport (TCP connection).
         """