Bump acorn from 6.4.0 to 6.4.2#7

dependabot[bot] wants to merge 1 commit intodevelopBracketSpace/Notification-Signature:developfrom

dependabot/npm_and_yarn/acorn-6.4.2BracketSpace/Notification-Signature:dependabot/npm_and_yarn/acorn-6.4.2Copy head branch name to clipboard