ignore node-config local files

[ztomm]

Node config is an often used module. It allows local configuration files that apply to the current platform and should not be tracked.

https://github.com/node-config/node-config/wiki/Configuration-Files#local-files

Reasons for making this change:

TODO

Links to documentation supporting these rule changes:

TODO

If this is a new template:

• Link to application or project’s homepage: TODO