chore(package): update gulp-babel to version 8.0.0-beta.2

Closes #12

Author: greenkeeper[bot]

package.json

@@ -25,7 +25,7 @@
     "chai": "^3.4.1",
     "eslint": "^3.10.2",
     "gulp": "^3.9.0",
-    "gulp-babel": "^6.1.1",
+    "gulp-babel": "^8.0.0-beta.2",
     "gulp-eslint": "^3.0.1",
     "gulp-mocha": "^3.0.1",
     "gulp-util": "^3.0.7",