Can't import using commonjs

[franciscolourenco]

Add support for loading with CommonJS syntax too AsyncComputed = require('vue-async-computed').

In the meanwhile a workaround is to use AsyncComputed = require('vue-async-computed').default

[foxbenjaminfox]

Sure, it makes sense to have support for CommonJS.

Luckily, it's only a babel plugin away.

I added the plugin to the project, so now it should properly work also with CommonJS.