chore: Update write-file-atomic

[coreyfarrell]

The intent is to release caching-transform@4.0.0 with this change.

[coveralls]

Pull Request Test Coverage Report for Build 66

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 64:	0.0%
Covered Lines:	50
Relevant Lines:	50

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💛 - Coveralls

[JaKXz]

If this is meant to be a breaking change, then it should be a fix! or feat! right?

I'm assuming of course there are breaking changes in write-file-atomic that affect caching-transform's functionality.

[coreyfarrell]

write-file-atomic is semver-major for two reasons.

1. It now requires node.js 8 (caching-transform#master already requires node.js 8)
2. option.Promise has been removed (no effect here as we don't use the async interface)

So this is non-breaking for caching-transform (note no changes to any *.js file). Technically it doesn't make much of a difference though as this repo has never followed conventional-commits, the release will be manual. And yes I plan to use conventional-commits once this release is complete.

[JaKXz]

@coreyfarrell That's what I thought [from my cursory knowledge of the two packages]... That's why I think this should just be a patch release and be marked fix: update write-file-atomic.

[coreyfarrell]

We're already in a semver-major cycle, we haven't released since node.js 6 was dropped.

[JaKXz]

Ah - I didn't know that..

[coreyfarrell]

@JaKXz is this OK then?