Fix NPM Cache Keys

[nicklozon]

SEMVER Update Type:

• Major
• Minor
• Patch

Description:

Motivation:

Cache key is not consistent between retrieval and saving jobs for npm - all save_cache steps are not respecting the cache-only-lockfile parameter.

Closes Issues:

• Orb behaviour with restore_cache does not match what source code says it should be doing #123
• cache-only-lockfile=true still uses package.json on save_cache step #115

Checklist:

• All new jobs, commands, executors, parameters have descriptions.
• Usage Example version numbers have been updated.
• Changelog has been updated.

[gavinsharp]

I have a similar PR up at #122.