Fixed deprecations for Elixir 0.12.2

  - Changed __FILE__ to __ENV__.file
  - Changed ->/2     to send/2
Updated .travis.yml to pull 0.12.2 elixir
Removed unnecessary requirement of test_helper and fixed up Elixir versions
Merge pull request #22 from Ortuna/dep-fixes

Fixed deprecations for Elixir 0.12.2