fix(package): update ember-cli-babel to version 7.4.1

Closes #14

Author: greenkeeper[bot]

package.json

@@ -28,7 +28,7 @@
     "broccoli-funnel": "2.0.1",
     "chalk": "2.4.1",
     "date-fns": "^1.29.0",
-    "ember-cli-babel": "^6.16.0",
+    "ember-cli-babel": "^7.4.1",
     "front-matter": "2.3.0",
     "glob": "7.1.3",
     "marked": "0.5.0",