Add GitLab CI

• Different set of boxes, there isn't a 7.2 in the current series and doesn't seem like that'll changes
• Correct PHPUnit version for PHP version, as Travis handles

Fixes #2 (closed)

.gitlab-ci.yml

@@ -37,7 +37,7 @@ PHPunit:PHP5.3:MySQL:
     - phpunit
 
 PHPunit:PHP5.6:MySQL:
-  image: php:5.6-alpine
+  image: php:5.6-stretch
   services:
     - mysql:5.6
   script:
@@ -46,7 +46,7 @@ PHPunit:PHP5.6:MySQL:
     - phpunit
 
 PHPunit:PHP7.0:MySQL:
-  image: php:7.0-alpine
+  image: php:7.0-stretch
   services:
     - mysql:5.6
   script:
@@ -55,7 +55,7 @@ PHPunit:PHP7.0:MySQL:
     - phpunit
 
 PHPunit:PHP7.1:MySQL:
-  image: php:7.1-alpine
+  image: php:7.1-stretch
   services:
     - mysql:5.6
   script:
@@ -64,7 +64,7 @@ PHPunit:PHP7.1:MySQL:
     - phpunit
 
 PHPunit:PHP7.2:MySQL:
-  image: php:7.2-alpine
+  image: php:7.2-stretch
   services:
     - mysql:5.6
   script: