fix: Type of multi_az_enabled variable (#36)

Author: egarbi

variables.tf

@@ -182,7 +182,7 @@ variable "preferred_cache_cluster_azs" {
 }
 
 variable "multi_az_enabled" {
-  type        = string
+  type        = bool
   description = "Specifies whether to enable Multi-AZ Support for the replication group. If true, `automatic_failover_enabled` must also be enabled. Defaults to false."
   default     = false
 }