remove trailing comma in package.json

Author: orteth01

package.json

@@ -39,7 +39,7 @@
     "pre-commit": "^1.2.2",
     "react": "^15.4.2",
     "react-addons-test-utils": "^15.4.2",
-    "react-dom": "^15.4.2",
+    "react-dom": "^15.4.2"
   },
   "repository": {
     "type": "git",