Breaking change removing bluebird

Hi, thanks for the great work on this lib.

The removal of bluebird introduce a breaking change. I think the version number of the lib should have changed accordingly.

Indeed, the spread method disappeared.

workbook.xlsx.readFile(file)
.then(() => {
  return Promise.all([
   asyncOpA(),
   asyncOpB()
  ])
})
.spread((resA, resB) => {
  //...
);

TypeError: [...].spread is not a function

I think the use of spread is very common for bluebird users. I my case, my build was broken by this minor version change.

Ideally, we should have the possibility to inject bluebird in ExcelJS to continue to use it.

[guyonroche]

Once again - sorry for the break. I have published 0.3.0 with the following two changes:

• A richer internal Promise implementation (that supports some of the bluebird extras including spread and map)
• Promise library dependency injection to allow you to restore bluebird if needed.

[AlexisNo]

Awesome! Thank for the quick fix. And again, thanks for the great job on this lib.