Mix Docker Versions Save

• Updated Erlang to 19.3.4 (#26 & e10bd904bb)
• Updated Elixir to 1.4.4 (#26 & e10bd904bb)
• Allow setting custom length of git sha (#24)

• Updated Elixir to 1.4.2

• Updated Alpine to 3.5
• Updated Erlang to 19.2
• Updated Elixir to 14.1
• New - Configurable tag template - thanks to @tlvenn
• New - Umbrella apps support - thanks to @lpil

Changes since v0.3.1

• #7 Add Phoenix deployment tips to Readme by @alex-kovshovik
• #8 Fixed compiler warnings for Elixir 1.4 by @aeons
• #11 Allow configuring path to dockerfiles by @aeons

Thanks @aeons! and @alex-kovshovik!

Changes since 0.2.0

• Updated distillery dependency to 1.1.0
• Added mix docker.customize task to edit the default Dockerfiles
• Improved README