Move intervention/image in require-dev section

Author: rkit

Diff for: composer.json

@@ -16,7 +16,6 @@
         "source": "https://github.com/rkit/filemanager-yii2"
     },
     "require": {
-        "intervention/image": "^2.3.2",
         "yiisoft/yii2": "^2.0"
     },
     "scripts": {
@@ -32,6 +31,7 @@
         }
     },
     "require-dev": {
+        "intervention/image": "^2.3.2",
         "phpunit/phpunit": "^4.8",
         "phpunit/dbunit": "^1.4"
     }