fix(package): update broccoli-merge-trees to version 2.0.0

https://greenkeeper.io/

package.json

@@ -32,7 +32,7 @@
     "broccoli-babel-transpiler": "^5.5.0",
     "broccoli-concat": "^3.1.1",
     "broccoli-funnel": "^1.0.1",
-    "broccoli-merge-trees": "^1.1.1",
+    "broccoli-merge-trees": "^2.0.0",
     "ember-cli-babel": "^5.1.7",
     "ember-cli-test-loader": "^1.1.0",
     "ember-cli-version-checker": "^1.1.6",