Support @ts-check for JS files

[Chris2011]

Please add this support for checking js files as well with TS definition files. This is supported since TS 2.3 but not supported in the plugin: https://github.com/Microsoft/TypeScript/wiki/Type-Checking-JavaScript-Files

Here is a little video about vue and TS, you only need the first 5-10 minutes to see the ts-check in action: https://www.vuemastery.com/conferences/vueconf-2018/vue-and-typescript-up-and-running-daniel-rosenwasser

So this is very handy for checking JS files as well, if you not want to change it to TS with a fully build process, etc.

Cheers

Chris