Simplify Jenkings build

Disable building docker-image.

Author: mbrendler

Dockerfile

@@ -1,4 +1,8 @@
 version: '3'
 services:
   app:
-    build: .
+    image: elixir:1.7.3-alpine
+    volumes:
+      - .:/code
+    working_dir: /code
+    entrypoint: /code/docker-entrypoint.sh

docker-compose.yml

@@ -2,6 +2,9 @@
 
 set -e
 
+mix local.hex --force
+mix local.rebar --force
+
 if [ "$1" = test ] ; then
   export MIX_ENV=test
   mix deps.get