[Security] Bump acorn from 6.4.0 to 6.4.2#23

dependabot-preview[bot] wants to merge 1 commit intomastermongodb-js/ns:masterfrom

dependabot/npm_and_yarn/acorn-6.4.2mongodb-js/ns:dependabot/npm_and_yarn/acorn-6.4.2Copy head branch name to clipboard