update require-dev dependency

Author: streamtw

composer.json

@@ -25,8 +25,10 @@
   "require": {
     "php": ">=5.4.0",
     "illuminate/support": ">=4.2.0",
-    "illuminate/foundation": ">=4.2.0",
-    "intervention/image": "2.*",
+    "intervention/image": "2.*"
+  },
+  "require-dev": {
+    "orchestra/testbench": "~3.0",
     "phpunit/phpunit": "~4.8"
   },
   "suggest": {