Update landing-zone.txt (#79)

"it is is" -> "it is"

Author: braz

source/landing-zone.txt

@@ -45,7 +45,7 @@ What is a Landing Zone?
 
 A landing zone is a framework for establishing a well-architected and
 pre-configured cloud environment for {+service+} that conforms to your organization's unique requirements across security, compliance, and governance. A landing zone is often a prerequisite for enterprises to
-move workloads to the cloud, and it is is often provisioned
+move workloads to the cloud, and it is often provisioned
 programmatically using an API or tools like Terraform.
 
 An {+service+} landing zone defines the default and minimum settings