fix build error for Docker image

[crsqq]

Fixed the following error when building the Docker image:

STEP 4/8: RUN pip git+https://github.com/zangobot/ember.git
ERROR: unknown command "git+https://github.com/zangobot/ember.git" 
Error: building at STEP "RUN pip git+https://github.com/zangobot/ember.git": while running runtime: exit status 1

[zangobot]

Thanks for the issue, but that repository is needed.
I will fix it soon.

[crsqq]

Appreciate the fast response.
https://github.com/zangobot/ember.git is already included in the requirements.txt, therefore removing it from the Dockerfile should not have any negative effect.

[zangobot]

Did you test this befire / after the modification to check whether it still works inside the container?