Use `browser.*` APIs when possible

[fregante]

https://github.com/crimx/webpack-target-webextension/blob/cbb1185e2e8935205a1f36d862bde80e1b96a3c3/lib/background.js#L3

• chrome is defined everywhere, so this piece of code has always used the chrome.* API
• There's no advantage in using the browser.* API in this case, it's still dealing with a callback

For this reason, I dropped the check and the duplicate code

[crimx]

Hi, first off, thanks for the PR!

The webpack-target-webextension, as its name suggests, is for WebExtension target. The chrome namespace is not part of the WebExtension spec. For the time being, major browser vendors also implement the chrome namespace because Google Chrome still dominates the web browser market and most of the current WebExtension APIs are heavily inspired by Chrome Extension.

For this reason, I would prefer using the browser namespace if possible and fallback to chrome.

[crimx]

Thanks!