add tslib dependency

[tellnes]

Fixes the same problem as stoplightio/yaml#45

I need this to make spectral work with yarn pnp mode.

Workaround is to add the following to .yarnrc.yml:

packageExtensions:
  '@stoplight/json-ref-readers@^1.2.1':
    dependencies:
      tslib: '^1.14.1'
  '@stoplight/lifecycle@^2.3.1':
    dependencies:
      tslib: '^1.14.1'

[stoplight-bot]

🎉 This PR is included in version 1.2.2 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀