Fixed bug's linter

Author: dosart

binary_search_tree/binary_serch_tree.py

@@ -20,7 +20,7 @@ def __len__(self):
         return self._count
 
     def is_empty(self):
-        """Returns True if tree is empty.
+        """Return True if tree is empty.
 
         Returns:
             bool: True if tree is empty else False