Bump upper bound to <0.22

[jtcohen6]

This is a:

• bug fix PR with no breaking changes — please ensure the base branch is master
• new functionality — please ensure the base branch is the latest dev/ branch
• a breaking change — please ensure the base branch is the latest dev/ branch
• non-breaking change to add new version compatibility

Description & motivation

• dbt v0.21 (currently in beta) shouldn't have any breaking changes for dbt-utils, so we can add compatibility as a patch release

Checklist

• I have verified that these changes work locally on the following warehouses (Note: it's okay if you do not have access to all warehouses, this helps us understand what has been covered)
  • BigQuery
  • Postgres
  • Redshift
  • Snowflake
• I have "dispatched" any new macro(s) so non-core adapters can also use them (e.g. the star() source)
• I have updated the README.md (if applicable)
• I have added tests & descriptions to my models (and macros if applicable)
• I have added an entry to CHANGELOG.md