TypeScript configuration files can't have comments

[JoshuaKGoldberg]

🐛 Bug Report

• tslint-to-eslint-config version: 0.1.8
• ESLint version: N/A
• Node version: N/A

Actual Behavior

If you've put non-JSON things in your tsconfig.json, such as comments, tslint-to-eslint-config --typescript tsconfig.json won't load the file. This is because the file is printed with cat on the CLI, then passed to JSON.parse in code.

Expected Behavior

TypeScript supports comments. We should too!

Reproduction

1. Create a tsconfig.json with comments in it
2. Run tslint-to-eslint-config --typescript tsconfig.json

[JoshuaKGoldberg]

Oh hey, https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-2.html#the-new---showconfig-flag: tsc --showConfig exists!