fix(package): update date-fns to version 2.2.1

Closes #30

Author: greenkeeper[bot]

package.json

@@ -27,7 +27,7 @@
     "broccoli-file-creator": "2.1.1",
     "broccoli-funnel": "2.0.1",
     "chalk": "2.4.1",
-    "date-fns": "^1.29.0",
+    "date-fns": "^2.2.1",
     "ember-cli-babel": "^6.16.0",
     "front-matter": "2.3.0",
     "glob": "7.1.3",