stl_query base model doesn't match Redshift

### Describe the bug
According to the documentation, the base models are supposed to closely match 1-1 with Redshift.

> Each of these base models maps 1-to-1 with the underlying Redshift table. Some renaming has been performed to make the field names grokable.

However the stl_query base model is missing a number of fields, including the querytxt. The full list of fields is at: https://docs.aws.amazon.com/redshift/latest/dg/r_STL_QUERY.html

Other base models may also be affected.

### Steps to reproduce
```
SELECT
q.querytxt
FROM {{ ref('redshift', 'stl_query') }} q
```

### Expected results
The model should build successfully.

### Actual results
" column q.querytxt does not exist"

### Screenshots and log output
None

### System information
**The contents of your `packages.yml` file:**
```
- package: fishtown-analytics/redshift
version: 0.4.1
```

**Which database are you using dbt with?**
- [ ] postgres
- [X] redshift
- [ ] bigquery
- [ ] snowflake
- [ ] other (specify: ____________)

**The output of `dbt --version`:**
```
installed version: 0.18.0
latest version: 0.19.1

Your version of dbt is out of date! You can find instructions for upgrading here:
https://docs.getdbt.com/docs/installation

Plugins:
- bigquery: 0.18.0
- snowflake: 0.18.0
- redshift: 0.18.0
- postgres: 0.18.0
```

**The operating system you're using:**
``` Ubuntu 18.04.5 LTS```

**The output of `python --version`:**
```Python 3.6.9```

### Additional context
None