So you've written your app in ES6 and you're using babel to transpile to ES5.
What do you do?
You could go down the route of requiring in the babel register at the top of your Gulpfile to get it to transpile on the fly.
But there is some built in functionality in Gulp which allows your to name your Gulpfile
Doing this will make Gulp look for a .babelrc and run your gulpfile via babel to get all the latest ES6/7 goodies you're using in the rest of your codebase.