Do not use one RUN command per apt-get and mkdir
In the Dockerfile you are using one RUN command per apt-get and mkdir command that is executed in the image. This is not optimum since each RUN command generates a own layer and the cleanup in the end is very inefficient. Changing to the structure in the attachment reduced the size of the image for me from 267 MB to 193 MB. This is a significant change and is in my mind worth the small change.
I do not have the rights to create a fork and upload a fix. If you agree you can either givve me that access or update based on the attached Dockerfile.
/MorganDockerfile