Address security warnings, upgrade dependencies, use npm-run-all.

[parkerziegler]

This PR was inspired a bit by #282, which incentivized me to see if we had any other security vulnerabilities. It turns out we did 😬Running yarn audit on master currently outputs the following:

After taking a look at the security warnings on npm, it became clear we could avoid these just by bumping a few of our dependencies. Running yarn audit on this branch yields no security warnings.

I also decided to make two other changes in this PR:

1. Use text as our command line coverage reporter for nyc. This gives us nice reporting on lines missing coverage and matches the Jest UI (which I find helpful when strategizing about what to test).

2. Include npm-run-all for our check and check-ci scripts. I like npm-run-all because it will detect what client you're using (npm or yarn) and use it for you to execute the scripts. I considered enforcing yarn here but realized this is often a polarizing enough decision that it might turn off contributors. For example, contributors can still npm install the project if they really want to, but if we used yarn in all of these package.json scripts, they flat out wouldn't work for npm users. npm-run-all is a nice in-between that keeps everyone happy. It exposes run-s which will run the commands in sequence (it also exposes run-p which will do things in parallel).

[ryan-roemer]

🚀 🛡