docker file changes #4619

Hey a couple of changes I found that helped me with building a docker image for my raspberry pi to run a knot

• Image changed to an arm version
• Was throwing an error on the compose example with cmd and worked with this
• Doesn't look like knot2/lexicons are there

I had also tried to pull the atcr image, but it looked to be 70+ days old and was not working for me.