Pass raw err to errorHandler callback

[mdreizin]

Hello,

It would be nice to use raw err in errorHandler callback:

Vue.use(AsyncComputed, {
errorHandler(err) {
console.log('Hey, an error!')
console.log('---')
console.log(err.message)
}
)

[foxbenjaminfox]

I've added a new option, useRawError. If you pass a truthy value for that option it will pass the raw error object to the error handler.

[mdreizin]

@foxbenjaminfox Thanks a lot.