Fix the python3 docker image
Fix the python3 docker image

The development requirements include pytest_girder which are not copied
into the docker file.  This was fixed in the python 2 version in an
earlier commit.

girder/girder,RafaelPalomar/girder,kotfic/girder,girder/girder,kotfic/girder,RafaelPalomar/girder,Kitware/girder,RafaelPalomar/girder,jbeezley/girder,jbeezley/girder,Kitware/girder,girder/girder,kotfic/girder,manthey/girder,kotfic/girder,Kitware/girder,jbeezley/girder,manthey/girder,RafaelPalomar/girder,Kitware/girder,manthey/girder,kotfic/girder,RafaelPalomar/girder,manthey/girder,jbeezley/girder,girder/girder