Fix private_cluster and master_ipv4_cidr_block in upgrade guide
Fix private_cluster and master_ipv4_cidr_block in upgrade guide

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/cc @pdecat
hashicorp/terraform-provider-google,terraform-providers/terraform-provider-google,ubschmidt2/terraform-provider-google,hashicorp/terraform-provider-google,ubschmidt2/terraform-provider-google,hashicorp/terraform-provider-google,terraform-providers/terraform-provider-google,terraform-providers/terraform-provider-google,terraform-providers/terraform-provider-google,terraform-providers/terraform-provider-google,hashicorp/terraform-provider-google,ubschmidt2/terraform-provider-google,ubschmidt2/terraform-provider-google