Update nodered/node-red Docker tag to v3.1.8

[renovate[bot]]

This PR contains the following updates:

Package	Update	Change
nodered/node-red	patch	3.1.7-18-minimal -> 3.1.8-18-minimal

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Release Notes

node-red/node-red-docker (nodered/node-red)

### [`v3.1.8`](https://togithub.com/node-red/node-red-docker/releases/tag/v3.1.8) [Compare Source](https://togithub.com/node-red/node-red-docker/compare/v3.1.7...v3.1.8) #### What's Changed - 🚀 Update to Node-RED 3.1.8 release by [@​knolleary](https://togithub.com/knolleary) in [https://github.com/node-red/node-red-docker/pull/424](https://togithub.com/node-red/node-red-docker/pull/424) **Full Changelog**: https://github.com/node-red/node-red-docker/compare/v3.1.7...v3.1.8

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