Drop PHP 5.3, WP no longer supports it

plugins/templates/before-script.yml

@@ -9,9 +9,7 @@ before_script:
     elif [[ $(php -v) =~ "PHP 7." ]]; then
       composer global require "phpunit/phpunit=6.1.*"
     elif [[ $(php -v) =~ "PHP 5.6" ]]; then
-      composer global require "phpunit/phpunit=5.4.*"
-    else
-      composer global require "phpunit/phpunit=4.8.*"
+      composer global require "phpunit/phpunit=5.7.*"
     fi
 
   # PHPUnit requirements

plugins/templates/matrix.yml

-PHPunit:PHP5.3:MySQL:
-  stage: test
-  variables:
-    WP_VERSION: '5.1'
-  image: containers.ethitter.com:443/docker/images/php:5.3
-  services:
-    - mysql:5.6
-  script:
-    - find . -type "f" -iname "*.php" | xargs -L "1" php -l
-    - phpunit
-
 PHPunit:PHP5.6:MySQL:
   stage: test
   image: containers.ethitter.com:443/docker/images/php:5.6