Update deps

[strzibny]

Update meck and poison to be used in newer projects.

I am using Elixir 1.9:

Erlang/OTP 21 [erts-10.3.5.5] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1] [hipe]

Elixir 1.9.0 (compiled with Erlang/OTP 21)

Tests pass locally for the new setup.

[maennchen]

Thanks @strzibny. Could you also raise the required elixir version in the mix.exs to at least 1.6 and adapt the travis-ci config accordingly?

[coveralls]

Coverage increased (+0.3%) to 89.744% when pulling d0db1a0 on strzibny:update-deps into f4530bf on jshmrtn:master.

[strzibny]

I updated it. I kept only OTP 21 since 22 is not compatible with Elixir 1.6 so the matrix fails.

[maennchen]

Thanks a lot! ❤️