Security vulnerability in S3 node package dependency

[emerick]

@diracdeltas mentioned that there's a security vulnerability in a dependency (mime < 1.4.1) used by brave/brave-core-crx-packager. Investigation turned up that this is due to a dependency on a (now abandoned) S3 module in brave/release-tools. That S3 module has been forked with updated dependencies (see andrewrk/node-s3-client#190), so we should update release-tools to use that newer S3 module.