Updated several test dependencies from years-old versions

[Antrikshy]

I noticed that several test dependencies were on years-old 0.x major versions of packages. npm audit pointed out several security vulnerabilities. These version bumps:

1. Bring down security audit results to 0 vulnerabilities.
2. Give us much newer and shinier Istanbul coverage reports.

npm test works as before. Tests pass.

[coveralls]

Coverage increased (+0.08%) to 94.318% when pulling 5c1f97c on Antrikshy:master into d7f4ea6 on peterolson:master.

[peterolson]

Thanks!