Remove useless Alpine dependencies

[gcauchon]

With this simplified setup, I can build and run the image without any SSL library/NIF related issues.

1. Build using the make target

> make build
docker build --build-arg APP_NAME=… --build-arg APP_VERSION=… --rm --tag mirego/accent -e 's/[:,]//g'`:latest .
Sending build context to Docker daemon  3.847MB
Step 1/32 : FROM elixir:1.8.1-alpine AS builder
 ---> 17ac2712c2de

[…]

Step 31/32 : ENTRYPOINT ["docker-entrypoint.sh"]
 ---> 5df139b07d1e
Step 32/32 : CMD ["foreground"]
 ---> 6a0e520e43c1
Successfully built 6a0e520e43c1
Successfully tagged accent:latest

2. And run the built image with docker-compose

> docker-compose up application
accent-postgres is up-to-date
Recreating accent ... done
Attaching to accent
accent         | Starting dependencies…
accent         | Starting repos…
accent         | Running migrations for accent
accent         | 02:29:42.633 [info] Already up
accent         | Running seed script for accent
accent         | Success!
accent         | WARNING: Node v10.14.2 is not tested against Ember CLI on your platform. We recommend that you use the most-recent "Active LTS" version of Node.js. See https://git.io/v7S5n for details.
accent         | 02:29:45.861 [info] Running Accent.Endpoint with cowboy 2.6.1 at http://localhost:4000
accent         | Could not start watchman
accent         | Visit https://ember-cli.com/user-guide/#watchman for more info.
accent         | ✨  Built in 2.49s.
accent         |
accent         | ../lib/accent-0.0.3/priv/static/jipt/index.js    11.84 KB    2.42s
accent         | Built project successfully. Stored in "/opt/accent/lib/accent-0.0.3/priv/static/webapp".
accent         | File sizes:
accent         |  - /opt/accent/lib/accent-0.0.3/priv/static/webapp/assets/accent-webapp-d17242bd0dfff3634ecee76683b8ee51.js: 661.31 KB (85.97 KB gzipped)
accent         |  - /opt/accent/lib/accent-0.0.3/priv/static/webapp/assets/accent-webapp-e8338c56e042cdcf5cc7a76daafd184a.css: 98.98 KB (17.42 KB gzipped)
accent         |  - /opt/accent/lib/accent-0.0.3/priv/static/webapp/assets/vendor-94b7623c6296fb48c65ba11e2e346514.js: 951.63 KB (256.26 KB gzipped)
accent         |  - /opt/accent/lib/accent-0.0.3/priv/static/webapp/assets/vendor-d41d8cd98f00b204e9800998ecf8427e.css: 0 B
accent         |  - /opt/accent/lib/accent-0.0.3/priv/static/webapp/ember-fetch/fastboot-fetch-805e176077930c98aec5834ae48bd0f2.js: 283 B (199 B gzipped)

[gcauchon]

@simonprev DO you have any idea why CI is stuck with:

Travis CI - Branch Expected — Waiting for status to be reported