Update nyc to version 6.4.2 🚀

[greenkeeperio-bot]

Hello :wave:

:rocket::rocket::rocket:

nyc just published its new version 6.4.2, which is not covered by your current version range.

If this pull request passes your tests you can publish your software with the latest version of nyc – otherwise use this branch to work on adaptions and fixes.

Happy fixing and merging :palm_tree:

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The new version differs by 9 commits .

• 1b625ff chore(release): 6.4.2
• bda6727 chore: upgrade standard-version
• b16053c fix: upgrade spawn-wrap to version that works with new shelljs (#242)
• 24f55e7 fix(update): update strip-bom to version 3.0.0 (#240)
• 693b797 chore(release): 6.4.1
• af0df0c docs: slight tweak to README
• 0946f82 fix: strip any duplicate extensions from --extension (#237)
• f775a2e docs: provide codecov instructions (#233)
• f320bc6 chore(package): update standard-version to version 2.1.2 (#228)

See the full diff.

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