fix(ts): 🐛 remove trailing comma in tsconfig.json

[Blfrg]

As discussed in quasar-testing/pull/117
When installing @quasar/testing-unit-jest with Typescript support it attempts to modify the tsconfig.json but a parsing error occurs.
Removing this trailing comma by default will help ensure new Quasar projects based on the starter kit will not experience the same error.

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