Update student-debt-calc and subdeps to address vulnerabilities

[Scotchester]

This updates student-debt-calc and reinstalls other dependencies to get downstream security updates into package-lock.json, and makes a small update to the .snyk policy file.

I also changed npm run snyk to just be the snyk command, so that you can run things other than just snyk test. For example, I used npm run snyk wizard after making this change to automate the dependency updates.

Checklist

• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows the standards laid out in the front end playbook
• Passes all existing automated tests
• New functions include new tests
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged
• Visually tested in supported browsers and devices
• Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)

[coveralls]

Coverage remained the same at 100.0% when pulling 9ba4abb on snyking into 642bb7f on master.