fix typo (#252)

docs/rpi_docker_monitor.md

@@ -174,7 +174,7 @@ There should be just the one item list.  Select "Docker and OS Metrics" from the
 
 
 ## Pi Hosted : Raspberry Pi Docker Monitoring Part 7
-[![Pi Hosted : Raspberry Pi Docker Monitoring Part 7](https://i.ytimg.com/vi/IoD3vFuep64/hqdefault.jpg?sqp=-oaymwEXCNACELwBSFryq4qpAwkIARUAAIhCGAE&rs=AOn4CLDBjV3a9aT7NV28n88mqqogOzLUww)](https://www.youtube.com/watch?v=IoD3vFuep64)4
+[![Pi Hosted : Raspberry Pi Docker Monitoring Part 7](https://i.ytimg.com/vi/IoD3vFuep64/hqdefault.jpg?sqp=-oaymwEXCNACELwBSFryq4qpAwkIARUAAIhCGAE&rs=AOn4CLDBjV3a9aT7NV28n88mqqogOzLUww)](https://www.youtube.com/watch?v=IoD3vFuep64)
 
 ## Acknowledgment
 * based on [Docker-Raspberry-PI-Monitoring](https://github.com/oijkn/Docker-Raspberry-PI-Monitoring) by Oijkn