Update deprecated Dockerfile instruction MAINTAINER to LABEL

[samlitowitz]

Resolves #10

[pszalko]

@samlitowitz Thank you for your support! I have removed support for deprecated PHP versions. Could you resolve conflicts before merge?

[samlitowitz]

@samlitowitz Thank you for your support! I have removed support for deprecated PHP versions. Could you resolve conflicts before merge?

Merge conflicts resolved.

Also, if you'd like to run the pipes, you need to add the label ci to a PR. This can be changed, but I had it by default so you control if and when pipes will run for a PR.

[pszalko]

@samlitowitz I've added ci label, i didn't notice it at first so thanks for the hint here :) Again, thank you for your commitment!