fix for settings.set subsequent updates

[sammachin]

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Proposed changes

By cloning the value the assert.deepEqual will now fail even for subsequent updates of the value without restarting Node-RED

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the forum/slack team.
• I have run grunt to verify the unit tests pass
• I have added suitable unit tests to cover the new/changed functionality

[coveralls]

Coverage decreased (-0.04%) to 77.51% when pulling a8d8540 on sammachin:sammachin-settings_set_fix into bcf1d98 on node-red:master.