upgrade to typescript 4.1 and silence yarn warnings

[dagda1]

Typescript 4.1 should have been the major version bump and not v4 but MS typescript do not do semver.

We can take advantage of some of the new features after this gets merged.

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: d5b9153c1c3f3edcbc8e27608f61580a2dc86978

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

| Name | Type | | --------------------- | ----- | | @frontside/tsconfig | Minor | | @frontside/typescript | Patch |

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions[bot]]

The preview packages of this pull request have been published. Click on the following packages for instructions on how to install them:

@frontside/eslint-config

--- Install using the following command: ```bash $ npm install @frontside/eslint-config@upgrade-to-typescript-4-1 ``` Or update your package.json file: ```bash { "@frontside/eslint-config": "upgrade-to-typescript-4-1" } ``` ---

eslint-plugin-prefer-let

--- Install using the following command: ```bash $ npm install eslint-plugin-prefer-let@upgrade-to-typescript-4-1 ``` Or update your package.json file: ```bash { "eslint-plugin-prefer-let": "upgrade-to-typescript-4-1" } ``` ---

@frontside/typescript

--- Install using the following command: ```bash $ npm install @frontside/typescript@upgrade-to-typescript-4-1 ``` Or update your package.json file: ```bash { "@frontside/typescript": "upgrade-to-typescript-4-1" } ``` ---

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