<issue_start><issue_comment>Title: Add Travis for Elixir 1.5, 1.6 and OTP 21
username_0: 
<issue_comment>username_1: 👋 Hey! I'm sorry for the lack of movement on this. I shouldn't have left this for so long without a reply. 

I am not currently writing Elixir at all, and therefore, I think it would be irresponsible of me to review PRs on this project. I just kept putting off reviewing the issues/PRs on this repo until I started writing Elixir again, but never got around to it. 

That is my mistake, and I'm really sorry about that 🙏. You put in the time to make this PR, and you deserve a response at the very least.

I've marked the project as "not being actively maintained" in the readme. Please feel free to fork it with a different name and put it up on hex with current fixes.