chore: remove Node.js 4 (EOL)

[DanielRuf]

Closes #79

[alexander-akait]

@DanielRuf Duplicate #80?

[codecov]

Codecov Report

Merging #81 into master will decrease coverage by 0.28%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #81      +/-   ##
==========================================
- Coverage    95.5%   95.22%   -0.29%     
==========================================
  Files           3        3              
  Lines         356      356              
  Branches       97       97              
==========================================
- Hits          340      339       -1     
- Misses         16       17       +1

Impacted Files	Coverage Δ
lib/DirectoryWatcher.js	95% <0%> (-0.42%)	⬇️

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[DanielRuf]

@DanielRuf Duplicate #80?

Not directly. This PR is just for removing the EOL Node.js version. The other is for adding Node.js 10 and removing Node.js 4 (which I will problably close then or force-push with just the Node.js 10 addition) to keep the changes atomic.

[realityking]

Partially duplicates #64. I suspect it hasn't been merged yet to avoid a semver-major release.

[DanielRuf]

Hm, you are right. Oversaw this one. Should I close my PR then?

[realityking]

I slightly prefer mine because it adds the engine to package.json but I'm not the PR police 😆