Add wp-cli/media-command as dev dependency

Author: schlessera

composer.json

@@ -18,6 +18,7 @@
         "wp-cli/cache-command": "^1.0",
         "wp-cli/db-command": "^1.3",
         "wp-cli/extension-command": "^1.2",
+        "wp-cli/media-command": "^1.1",
         "wp-cli/wp-cli-tests": "^0"
     },
     "config": {