Fix sourcemap support

[billowz]

Description

• fix sourcemap
• update dependencies
• update readme.md

Related Issue

closes #21

Motivation and Context

the sourceMap option not work (#21)

How Has This Been Tested?

I have add a test to check the generated source map from rollup

[benmccann]

@artberri any change you'd be able to take a look at this PR?

[doppelganger9]

Hi,

This PR + a new published NPM version will help solving - in a clean way - this issue on another repository : bahmutov/coverage-example-svelte#1

In the meantime, we'll reference the rc branch from @billowz forked repo.
npm install --save-dev https://github.com/billowz/rollup-plugin-istanbul#rc

[niksy]

What is the status of this PR? Can we get this merged?

[artberri]

I was a bit 'out' of this package, I'll try to review this during this week if possible.

[artberri]

Hi @billowz the new version 3.0.0 that I've already published in the npm registry should fix the bug.

The PR has been automatically closed because I changed the default branch name from master to main. Anyway, I didn't want to merge it because it was a bit outdated (my fault, of course). I don't think the extensions option is needed neither.

So, I've finally coded the fix myself based on your work. THANK YOU VERY MUCH FOR YOUR TIME.

/cc @niksy