Update dependency @sourcegraph/tslint-config to ^12.1.0

Created by: renovate[bot]

This PR contains the following updates:

Package	Type	Update	New value	References	Sourcegraph
@​sourcegraph/tslint-config	devDependencies	minor	^12.1.0	source

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Release Notes

sourcegraph/tslint-config

v12.1.0

Compare Source

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Renovate configuration

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