rebar2 dependency

Any chance we can get this updated to rebar3? rebar2 is dead.
```
07:41:12 $USERNAME@$COMPUTERNAME gdauthex ±|dev ✗|→ mix deps.compile --force
===> Compiling parse_trans
Could not find "rebar", which is needed to build dependency :base64url
I can install a local copy which is just used by Mix
Shall I install rebar? (if running non-interactively, use "mix local.rebar --force") [Yn]
```