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

Closes #86

Author: greenkeeper[bot]

package.json

@@ -91,7 +91,7 @@
     "espower": "^2.0.0",
     "gulp": "gulpjs/gulp#4.0",
     "gulp-ava": "^0.14.1",
-    "gulp-babel": "^6.1.2",
+    "gulp-babel": "^8.0.0",
     "gulp-cached": "^1.1.0",
     "gulp-newer": "^1.3.0",
     "gulp-optimize-js": "^1.1.0",