chore(deps): update dependency tslint to ^6.1.2

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	New value	References	Sourcegraph
tslint (source)	devDependencies	patch	^6.1.2	homepage, source

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Release Notes

palantir/tslint

### [`v6.1.2`](https://togithub.com/palantir/tslint/blob/master/CHANGELOG.md#v612) [Compare Source](https://togithub.com/palantir/tslint/compare/6.1.1...6.1.2) - [bugfix] restore typings compatibility with TS < 3.8 ([#​4933](https://togithub.com/palantir/tslint/issues/4933))

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