TASK: Migrate to smaller alpine images

* To have faster downloads, smaller images, simpler installs

.gitlab-ci.yml

@@ -1,11 +1,5 @@
 before_script:
-  - >
-    apt-get update
-    && apt-get install -y
-    make
-    wget
-    --no-install-recommends
-    && rm -r /var/lib/apt/lists/*
+  - apk add --no-cache make wget git
   - make install-composer
   - make install
 
@@ -13,13 +7,13 @@ stages:
   - test
 
 test:5.6:
-  image: php:5.6
+  image: php:5.6-alpine
   stage: test
   script:
     - ./vendor/bin/phpunit
 
 test:7.0:
-  image: php:7.0
+  image: php:7.0-alpine
   stage: test
   script:
     - ./vendor/bin/phpunit