Add fs-extra module to dependencies in @node-red/util module

[kazuhitoyokoi]

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

Proposed changes

When I tried the electron Node-RED using Node-RED v2.0 beta 2, I encountered a startup error.

I found that this problem came from a lack of dependencies in the @node-red/util module. Therefore, I added the fs-extra module as dependencies in the @node-red/util module. (Strangely, this problem didn't occur using Node-RED v1.3.5).

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 remained the same at 67.604% when pulling e81a6db on kazuhitoyokoi:dev-fixdependencies into b2f5a25 on node-red:dev.

[knolleary]

This needs fixing in master as well.

[kazuhitoyokoi]

@knolleary Thank you for the fixing in the master branch. :)

[kazuhitoyokoi]

@knolleary For dev and master branches, I submitted other pull requests related to this. Could you check them?