Fix the time_jump_callback signature. (#711)

Because it accesses object data, the first argument
must be 'self'.

Signed-off-by: Chris Lalancette <clalancette@gmail.com>

tf2_ros_py/tf2_ros/buffer.py

@@ -104,7 +104,7 @@ def __get_frames(
     ) -> FrameGraphSrvResponse:
         return FrameGraph.Response(frame_yaml=self.all_frames_as_yaml())
 
-    def time_jump_callback(time_jump: TimeJump):
+    def time_jump_callback(self, time_jump: TimeJump):
         rclpy.logging.get_logger("tf2_buffer").warning("Detected jump back in time. Clearing tf buffer.")
         self.clear()