Add support for building multiple PHP versions on docker

Dockerfile

@@ -1,4 +1,5 @@
-FROM php:cli
+ARG version=cli
+FROM php:$version
 
 COPY . /var/www
 WORKDIR /var/www

docker-compose.yml

@@ -1,4 +1,4 @@
-version: '3'
+version: '2.1'
 services:
   php:
     build:
@@ -9,3 +9,23 @@ services:
       - ./data:/var/www/data
       - ./tests:/var/www/tests
       - ./phpunit.xml.dist:/var/www/phpunit.xml.dist
+  '7.2':
+    extends: php
+    build:
+      args:
+        version: 7.2-cli
+  '7.1':
+    extends: php
+    build:
+      args:
+        version: 7.1-cli
+  '7.0':
+    extends: php
+    build:
+      args:
+        version: 7.0-cli
+  '5.6':
+    extends: php
+    build:
+      args:
+        version: 5.6-cli

makefile

@@ -1,3 +1,5 @@
+PHP ?= '7.2'
+
 docs:
 	wget http://apigen.org/apigen.phar
 	chmod +x apigen.phar
@@ -8,12 +10,12 @@ image:
 	docker build -t matthiasmullie/minify .
 
 up:
-	docker-compose up -d php
+	docker-compose up -d $(PHP)
 
 down:
-	docker-compose stop -t0 php
+	docker-compose stop -t0 $(PHP)
 
 test:
 	[ $(UP) -eq 1 ] && make up || true
-	$(eval cmd='docker-compose run php vendor/bin/phpunit')
+	$(eval cmd='docker-compose run $(PHP) vendor/bin/phpunit')
 	eval $(cmd); status=$$?; [ $(DOWN) -eq 1 ] && make down; exit $$status