Bump mongoose from 6.0.2 to 6.4.6 in /backend#2

dependabot[bot] wants to merge 1 commit intomasterAndrewJBateman/mern-stack-tracker:masterfrom

dependabot/npm_and_yarn/backend/mongoose-6.4.6AndrewJBateman/mern-stack-tracker:dependabot/npm_and_yarn/backend/mongoose-6.4.6Copy head branch name to clipboard