chore(deps): update dependency gulp-babel to v8

Author: renovate-bot

package.json

@@ -14,7 +14,7 @@
     "coveralls": "^2.11.2",
     "del": "^2.0.2",
     "gulp": "gulpjs/gulp#4.0",
-    "gulp-babel": "^5.3.0",
+    "gulp-babel": "8.0.0",
     "gulp-concat": "^2.5.2",
     "gulp-footer": "^1.0.5",
     "gulp-header": "^1.2.2",