Add dry run mode to `npm version`

[cincodenada]

Purpose (TL;DR)

Adds a dry-run mode to our npm version scripts

Background (Problem in detail) - optional

Currently there's no easy way to test npm version commands without actually publishing a release and pushing the updated branches to GitHub, which we obviously don't want to do.

Solution

The post-version script now looks for a DRY_RUN environment variable, which if set, will cause it to skip the following steps in the release process:

• Actually publishing to npm (it runs npm publish --dry-run instead)
• Pushing the branches up to remote

How to verify - mandatory

Run DRY_RUN=1 npm version and it should not actually publish a release! You may want to manually edit postversion.sh to disable the npm publish in the non-dry-run path though, just in case things are broken somehow.

Checklist for author

• [x] npm run lint passes
• [x] References to standard library functions are cached.

[codecov[bot]]

Codecov Report

Merging #2436 (c6aa2d3) into master (a57bbf6) will not change coverage. The diff coverage is n/a.

:exclamation: Current head c6aa2d3 differs from pull request most recent head 1882051. Consider uploading reports for the commit 1882051 to get more accurate results

@@           Coverage Diff           @@
##           master    #2436   +/-   ##
=======================================
  Coverage   96.01%   96.01%           
=======================================
  Files          41       41           
  Lines        1906     1906           
=======================================
  Hits         1830     1830           
  Misses         76       76           

Flag	Coverage Δ
unit	96.01% <ø> (ø)

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