fix: Migrate from istanbul to nyc

[YasharF]

Per https://www.npmjs.com/package/istanbul the package has been deprecated.

This module is no longer maintained, try this instead: npm i nyc Visit https://istanbul.js.org/integrations for other alternatives.

This change will also fix the following warnings when running npm install

npm WARN deprecated istanbul@0.4.5: This module is no longer maintained, try this instead:
npm WARN deprecated npm i nyc
npm WARN deprecated Visit https://istanbul.js.org/integrations for other alternatives.

[YasharF]

After merging this and other open PR's, can you also bump the package version and push the changes to the npm.com repo:

• Bump to v1.1.0 at https://github.com/jstransformers/test-jstransformer/blob/master/package.json#L3
• Update https://github.com/jstransformers/test-jstransformer/blob/master/HISTORY.md
• Git tag 1.1.0
• npm publish

[RobLoach]

Nice.

[RobLoach]

Istanbul is referenced in the bin....

foreground(process.argv[0], [require.resolve('istanbul/lib/cli'), 'cover', __filename]);