Revert "Update Dockerfile"

This reverts commit b0c90054
3 jobs for master in 3 minutes and 34 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build
passed #3288
build_python2.7

00:03:34

passed #3289
build_python3.6

00:03:03

passed #3290
build_python3.8

00:02:27