Add globalObject to webpack config output

[jasonbarry]

This PR fixes #38 by adding the globalObject output setting in the common webpack config. Per webpack's docs:

When targeting a library, especially when libraryTarget is 'umd', this option indicates what global object will be used to mount the library. To make UMD build available on both browsers and Node.js, set output.globalObject option to 'this'. Defaults to self for Web-like targets.

This change replaces the instance of self in the built output to become this, which works in both node and browser environments.

[jasonbarry]

This also fixes #56 by letting you import the library like this:

import QRCodeStyling from 'qr-code-styling'

[cayasso]

Any update on this?

[KiT-Maverik]

Any updates on this?