Attempt to use lighter docker images for gitlab builds

.gitlab-ci.yml

@@ -5,7 +5,7 @@ before_script:
     - php composer.phar install --ignore-platform-reqs
 services:
     - mysql:latest
-    - postgres:latest
+    - postgres:alpine
 
 variables:
     MYSQL_ROOT_PASSWORD: foo-bar-baz
@@ -17,11 +17,11 @@ variables:
     POSTGRES_PASSWORD: test
 
 test:7.1:
-    image: php:7.1
+    image: php:7.1-alpine
     script:
       - vendor/bin/phpunit -c build  --no-coverage
 
 test:7.2:
-    image: php:7.2
+    image: php:7.2-alpine
     script:
       - vendor/bin/phpunit -c build  --no-coverage

build/docker_install.sh

@@ -9,8 +9,10 @@ DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 set -xe
 
 # Install git (the php image doesn't have it) which is required by composer
-apt-get update -yqq
+echo -e 'http://dl-cdn.alpinelinux.org/alpine/edge/main\nhttp://dl-cdn.alpinelinux.org/alpine/edge/community\nhttp://dl-cdn.alpinelinux.org/alpine/edge/testing' > /etc/apk/repositories
-apt-get install git libpq-dev unzip -yqq
+apk add --no-cache \
+	curl \
+	git
 
 # Install phpunit, the tool that we will use for testing
 curl -Lo /usr/local/bin/phpunit https://phar.phpunit.de/phpunit.phar