[0.5.0] Support dbt-labs/dbt_utils v0.7.0

[jtcohen6]

• Bump the upper bound on dbt_utils to <0.8.0, to support dbt-utils v0.7.0 (which is required for use with dbt v0.20.0)
• ❗ Update the dependency from fishtown-analytics/dbt_utils to dbt-labs/dbt_utils. This is a breaking-ish change
  (https://discourse.getdbt.com/t/packages-dbt-labs-in-the-dbt-hub/2711) if users have other packages that install / depend on fishtown-analytics/dbt_utils. To avoid bad outcomes, I think this should require a minor version bump.

For the sake of clarity, we could choose to make a stronger delineation and have v0.5.0 of this package require dbt>=0.20.0 and dbt-utils>=0.7.0. It's not strictly required; someone could use v0.5.0 with dbt v0.19.0, so long as they pin dbt-labs/dbt_utils v0.6.6 and don't have another package that requires it as fishtown-analytics/dbt_utils.

[alanmcruickshank]

Nice 👍 . I like your suggestion of being stricter on clarity for 0.20.0