Fix issue with non-supporting ES6 browsers (e.g. IE11) and webpack

[Zhephyr54]

I tried to use your library in one of my project (using Webpack and targetting ES5) and I noticed that using it resulted in a syntax error in IE11.
After investigating about this issue, I found the root cause is that the javascript file being used in the end is overlayscrollbars-react.esm.js which is using ES6 syntax. This esm build should not be used in this situation.

This choice is being made by Webpack because it is picking conditional exports from the package.json file in this priority order: browser, module, main. As your package.json isn't specifying any browser conditional export, the module is picked and the esm build file is imported instead of the ES5 compliant one overlayscrollbars-react.js in my case.

Here are some external discussions regarding this issue happening for other libraries:
webpack/webpack#5756 (comment)
fabiospampinato/cash#291

Useful information regarding the browser property: https://docs.npmjs.com/files/package.json#browser

I was able to handle this issue on my side by specifying the resolve.mainFields property inside the webpack.config.js but this can cause other dependencies to break and can be fixed easily on your side with this PR.

Note: I did the same change for ngx and vue as the issue would be the same.

[KingSora]

Good day!

Thanks a lot, I didn't know that until now. I'll try to publish the new version as fast as possible.

[KingSora]

@Zhephyr54 The new versions are out now, so you can use your own fix. :)

[Zhephyr54]

Thanks a lot for your quick reaction :)

[KingSora]

@Zhephyr54 I wanna let you know, that I'll revert this PR in the next update. Please check out the reasons here: #190