Fix typo

docs/userguide/lifted_ops.rst

@@ -50,7 +50,7 @@ The ``.`` operator works similarly to ``[]`` described above:
     fut = my_app
     assert fut.x.result() == fut.result().x
 
-Attributes beginning with ``_`` are not lifted as thus usually indicates an
+Attributes beginning with ``_`` are not lifted as this usually indicates an
 attribute that is used for internal purposes, and to try to avoid mixing
 protocols (such as iteration in for loops) defined on AppFutures vs protocols
 defined on the underlying result object.