Fix CI server

[Piotr Żelazko]

Travis is now using old Elixir and OTP, which causes mix test command to fail, but Travis still thinks that it has not failed, because it checks status of the last command and the command is the whole script, which last line simply kills parity so it is always successful.

The command "bash travis_test.sh" exited with 0.

[Harley Swick]

Thanks for pointing this out. I'll take a look at it.