Update composer.json

Add bin/mage to composer. See http://getcomposer.org/doc/articles/vendor-binaries.md.

composer.json

@@ -7,5 +7,8 @@
     "keywords": "deployment",
     "require": {
         "php": ">=5.3"
-    }
+    },
+    "bin": [
+        "bin/mage"
+    ]
 }