Minimize transpilation of async functions

[acjay]

With the default Next.js Babel settings, async functions are transpiled to generators, which are further translated to Regenerator. This makes debugging more awkward than it needs to be.

I can't figure out how to disable this behavior with Next.js's Babel and Webpack configurations (see also this Stack Overflow question). But it seems like this sort of change would be useful for most people using electron-next, since the JS runtime support needs are tightly targeted for a pure Electron app.