[0.4.0] Upgrade to dbt v0.20

[jtcohen6]

(same basic story as fivetran/dbt_hubspot_source#46)

Are you a current Fivetran customer?
Jeremy Cohen, dbt Labs, yes!

What change(s) does this PR introduce?

• Require fivetran_utils: [">=0.2.0", "<0.3.0"]. Lower + upper since you have full control over this package, and can release it whenever you need.
• Require dbt >= 0.20.0. Just a lower bound because we can rely on dbt_utils (via fivetran_utils) to hold the upper dbt bound for us.
• Bump project version (cosmetic only)
• Bump dbt version in integration tests, and remove dbt version requirement from integration tests dbt_project.yml — this will just use the dbt version requirement in the packages it depends on

Does this PR introduce a breaking change?

• Yes (please provide breaking change details below.)
• No (please provide explanation how the change is non breaking below.)

Is this PR in response to a previously created Issue

• Yes, Issue [link issue number here]
• No

How did you test the PR changes?

• CircleCi
• Other (please provide additional testing details below)

Select which warehouse(s) were used to test the PR

• BigQuery
• Redshift
• Snowflake
• Postgres
• Databricks
• Other (provide details below)

I ran this on Postgres, everything passed, with one tiny change: I needed to wrap quotes around the default column in brand_data, since default is a reserved word in Postgres.

dbt deps
dbt seed
dbt run
dbt test

As before, happy to run against the other warehouses if you'd like. With an update like this, if the package parses/compiles/runs right on one, it ought to across the board.

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[jtcohen6]

I realize I accidentally included an edit to integration_tests/data/brand_data.csv that wrapped a column named default in quotes. This was needed to run integration tests on Postgres locally, but it doesn't make sense to include as part of this PR.

[fivetran-joemarkiewicz]

Thanks again for tackling this PR for dbt 0.20.0 compatibility 🕺

Before I merge to master I am going to approve and merge to the staging feature/jtcohen-dbt20-upgrade branch to check that the changes pass our cross warehouse tests.