update minimal click version to allow case_sensitive option

[rom1gal]

When using the CLI within specific environment (in my case an Azure DevOps agent running Ubuntu 18.06) some librairies need to be upgraded for the CLI to work properly (click when running the 6.7 version triggers the stacktrace displayed here : #337)

[andrewmchen]

Thanks for reporting and thank you for the fix. I'm wondering if we can just remove this option instead. https://github.com/databricks/databricks-cli/blob/master/databricks_cli/secrets/cli.py#L54.

@sushi1998

[rom1gal]

Actually I do not understand the purpose of that option since it is currently not possible to create a Azure KV-backed secret scope :/

[pietern]

The case_sensitive argument was removed in #347.

However, in the mean time we merged #471 which depends on click >= 7.0 for a different reason.