Migrate from tslint to eslint

[kamilmysliwiec]

Description

This PR migrates the starter project from tslint to eslint. We don't have to follow/extend any external style guide (e.g. Airbnb), TypeScript defaults (and recommendations) seems to be in line with the framework best practices.

[nechar]

Thanks, @kamilmysliwiec for the update.

Just felt that it was worth mentioning to the community for devs who have an existing application containing TSLint.

Problem:
It was extremely difficult to get the configuration right when trying to upgrade manually (by uninstalling TSLint and then installing ESLint)

Solution:
Using the latest NestJS CLI v 6.14.2 (as of 28 Feb 2020), I was able to get the correct ESLint configuration and the compatible plugins that worked perfectly the nest application. (By creating a new NestJS application nest new app-name)
After that, all you need to do is

• copy the new .eslint.js file and paste into your existing NestJS application.
• delete the existing .tslint.json file
• install the related ESLint packages that are listed in package.json into your existing NestJS application. (There are several of them)
• uninstall TSLint