Support editor to return PromiseLike object

[superfreeeee]

Enable editor to return Promise object which contains new JSON object as its value

[superfreeeee]

@rejas hello there, can you please checkout this pull request for me, I really need this feature in my own project

[rejas]

@superfreeeee Unfortunately I dont have aproject anymore where I use this. So you have to tell me please: is this a breaking change or do existing projects have to adjust if I merge this?

[superfreeeee]

@superfreeeee Unfortunately I dont have aproject anymore where I use this. So you have to tell me please: is this a breaking change or do existing projects have to adjust if I merge this?

@rejas There is no breaking change, but enable developers to return PromiseLike object and fit into node Readable stream created by gulp.
After this update, those who already use this plugin won't need to change there code, but they can change editor function to async if they need it. Please check it out.

[rejas]

Thanks for the PR!