Migrate tslint to eslint

[aorinevo]

Introduction

In 2019 a decision was made to deprecate TSLint in favor of ESLint (see [1]).

To that end, Shepherd should target migrating from TSLint to ESLint in 2020.

Acceptance Criteria

• Deprecate TSLint in favor of ESLint
• Update README to account for this change

Notes

• Several migration strategies have been published online. For example, [2].

References

1. https://medium.com/palantir/tslint-in-2019-1a144c2317a9
2. https://medium.com/@KevinBGreene/migrating-from-tslint-to-eslint-6382f8bd3b6