Running Phoenix server in Travis CI

If you are looking to start your phoenix server while running travis, the server won't start by default.

For example try running: `MIX_ENV=test mix phoenix.server`

Nothing will happen.

To be able to run the above command, you will need to change `false` to `true` in `config/test.exs`:
```elixir
config :app, App.Endpoint,
http: [port: 4001],
server: false
```

Now `MIX_ENV=test mix phoenix.server` will be running on `http://localhost:4001`