modified docker file to support update on alpine package for pip

[nigifabio]

Hi,
first of all, amazing project, i'm trying to implement here at work, but i'm still in testing phase,there is a small glitch on the Docker package now it build properly, let me know if it's ok and i hope to support the project more in the future :)

[mwielgoszewski]

Hi @nigifabio, thanks for the submission! I'm not a Docker user so I have no way of verifying py-pip vs py2-pip. Do you have a reference to Docker documentation or changelog that suggests this command was renamed?

[nigifabio]

Sure,
if you try to build the image from scratch you will find out is not building anymore, is due to a change in the package manager of alpine here a reference rroemhild/docker-mailpile#3

Ah really good work with doorman locking forward to push more commit since now :)