Fix some dependency vulnerabilities

[wdoug]

After running npm install with node 10, npm reported a bunch of security vulnerabilities in the installed dependencies:

Running npm audit fix fixed most of the issues and things still seem to work fine. The remaining 60 vulnerabilities require upgrading dependencies with breaking changes:

found 75 vulnerabilities (65 low, 2 moderate, 8 high) in 36983 scanned packages
  73 vulnerabilities require semver-major dependency updates.
  2 vulnerabilities require manual review. See the full report for details.

When I tried upgrading those dependencies things broke so they will take a little bit more work to fix. Here is a pull request with the first autofixed vulnerabilities to start.