fix(contracts): includes artifacts in @aragon/osx-artifacts package

[mathewmeconry]

Description

With the switch to rollupjs we don't include the artifacts in the @aragon/osx-artifacts package anymore. This pull fixes this issue so that they are included again.

this pull also bumps the version of @aragon/osx-artifacts and @aragon/osx-ethers to 1.3.1

Task ID: OS-951

Type of change

See the framework lifecylce in packages/contracts/docs/framework-lifecycle to decide what kind of change this pull request is.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• [ ] I have selected the correct base branch.
• [ ] I have performed a self-review of my own code.
• [ ] I have commented my code, particularly in hard-to-understand areas.
• [ ] My changes generate no new warnings.
• [ ] Any dependent changes have been merged and published in downstream modules.
• [ ] I ran all tests with success and extended them if necessary.
• [ ] I have updated the CHANGELOG.md file in the root folder.
• [ ] I have updated the DEPLOYMENT_CHECKLIST file in the root folder.
• [ ] I have updated the UPDATE_CHECKLIST file in the root folder.