SECURITY: update library versions to plug vulns

STUB

• there are some vulns effecting npm packages we depend on
  • we don't actually use any of the codepaths discussed in the relevant CVEs
  • but as a matter of course we should update our dependencies every now and again!
• when we update be sure that the following libraries meet or exceed the following versions:
  • sequelize (bump to >5.15.1)
  • lodash (bump to >= 4.17.12)
  • eslint-utils (bump to >= 1.4.1)
  • set-value (bump to >2.0.1)
  • mixin-deep (bump to >= 1.3.2)