Update MV Drop Materialization with cascade

[amychen1776]

resolves #
[docs dbt-labs/docs.getdbt.com/#](#642)

Problem

This will update the materialization to include cascade so it will take care of dependencies.

Solution

I added one word :)

Checklist

• [x ] I have read the contributing guide and understand what's expected of me
• [x ] I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• [x ] This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the dbt-redshift contributing guide.