Change references from TSLint to ESLint

[Alex Böhm]

We should change the references from TSLint to ESLint as TSLint has been deprecated as of 2019.

See https://palantir.github.io/tslint:

⚠️ TSLint is deprecated.

See this issue for more details: Roadmap: TSLint → ESLint. If you're interested in helping with the TSLint/ESLint migration, please check out our OSS Fellowship program.

[Dumitru]

Good catch!
A PR is welcome 🚀 !

[Alex Böhm]

I will tackle it in the next few weeks.