Fix link in update guide and add version

[themantissa]

Description

Fix link in update guide for advanced_cluster (was clusters) and add version due to guide issue.

Link to any related issue(s):

Type of change:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Documentation fix/enhancement

Required Checklist:

• I have signed the MongoDB CLA
• I have read the Terraform contribution guidelines
• I have added tests that prove my fix is effective or that my feature works per HashiCorp requirements
• I have added any necessary documentation (if appropriate)
• I have run make fmt and formatted my code

Further comments

[jwilliams-mongo]

@themantissa lgtm

[jwilliams-mongo]

should we update the version number here? and also below on line 26?

Suggested change

	The Terraform MongoDB Atlas Provider version 1.1.0 has a number of new and exciting features and changes.
	The Terraform MongoDB Atlas Provider version 1.1.1 has a number of new and exciting features and changes.