ci: use Node.js v10 image

[stephenmathieson]

This helps ensure we're using an up-to-date version of npm.

Reviewer checks

Required fields, to be filled out by PR reviewer(s)

• [x] Follows the commit message policy, appropriate for next version
• [x] Has documentation updated, a DU ticket, or requires no documentation change
• [x] Includes new tests, or was unnecessary
• [x] Code is reviewed for security by: @wilcofiers