fix: Update eslint to v7

[RDIL]

What it does

ESLint (and its typescript counterpart) have been updated. This really just removes deprecated rules and updates the recommended presets, so not too much here.

How to test

Tests passed locally.

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

[akosyakov]

It does not seem that you pushed updated yarn.lock.

[RDIL]

Fixed. My Yarn version was newer than Travis's.

[vince-fugnitto]

I don't really see the benefit of bumping the versions but losing functionality by removing
"@typescript-eslint/class-name-casing": "error". We should find a solution which does not remove one of our rules as it will lead to poorer code quality and issues down the road with naming.

If we are to bump, we should make sure that the rule still works correctly.

For example:

export class a { }

reports an error on master but not this pull-request.

Class 'a' must be PascalCased. eslint(@typescript-eslint/class-name-casing)

---

If we are to remove the dependency, then we also need to make sure to clean up the rule as it currently complains.

[akosyakov]

There seems to be another rule typescript-eslint/typescript-eslint#2251.

btw I've already upgraded eslint in #7908 I think I've done it to enable latest deprecation rule which was lost during migration from tslint. I would prefer to have deprecation rule working than @typescript-eslint/class-name-casing. I am not even sure we have latter rule with tslint before.

[RDIL]

Alright. I'm just trying to keep everything up-to-date in the toolchain, so I'll look into this or find something else that needs updating.

[marcdumais-work]

Alright. I'm just trying to keep everything up-to-date in the toolchain, so I'll look into this or find something else that needs updating.

Thanks @RDIL