Avoid using string literals in type annotations (#2294)

third_party/2/pymssql.pyi

@@ -11,7 +11,7 @@ class Connection(object):
     def autocommit(self, status: bool) -> None: ...
     def close(self) -> None: ...
     def commit(self) -> None: ...
-    def cursor(self) -> 'Cursor': ...
+    def cursor(self) -> Cursor: ...
     def rollback(self) -> None: ...
 
 class Cursor(object):