chore(package): update broccoli-concat to version 3.1.0

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -17,7 +17,7 @@
   ],
   "devDependencies": {
     "broccoli-babel-transpiler": "^5.6.1",
-    "broccoli-concat": "^3.0.2",
+    "broccoli-concat": "^3.1.0",
     "broccoli-merge-trees": "^1.1.1",
     "broccoli-rollup": "^1.0.2",
     "broccoli-stew": "^1.2.0",