Necessary change to git remote module URL format.

Basically changing things around and removing double slashes.
AS per hashicorp/terraform#21107 (comment)

routes/main.tf

@@ -70,7 +70,7 @@ locals {
 # MODULES
 ############################
 module "route-to-internet" {
-  source                 = "git::https://github.com/ministryofjustice/hmpps-terraform-modules.git?ref=master//modules//routes//internetgateway"
+  source                 = "git::https://github.com/ministryofjustice/hmpps-terraform-modules.git//modules/routes/internetgateway?ref=master"
   route_table_id         = "${local.route_table_public_ids}"
   destination_cidr_block = "${local.destination_cidr_blocks}"
   gateway_id             = "${data.terraform_remote_state.internetgateway.internetgateway_env_igw_id}"
@@ -81,7 +81,7 @@ module "route-to-internet" {
 # ## be deleted.
 # # PRIVATE NETWORK
 module "route-private-to-nat" {
-  source                 = "git::https://github.com/ministryofjustice/hmpps-terraform-modules.git?ref=master//modules//routes//natgateway"
+  source                 = "git::https://github.com/ministryofjustice/hmpps-terraform-modules.git//modules/routes/natgateway?ref=master"
   route_table_id         = "${local.route_table_private_ids}"
   destination_cidr_block = "${local.destination_cidr_blocks}"
   nat_gateway_id         = "${local.nat_gateway_ids}"
@@ -92,7 +92,7 @@ module "route-private-to-nat" {
 # ## be deleted.
 # # DB NETWORK
 module "route-db-to-nat" {
-  source                 = "git::https://github.com/ministryofjustice/hmpps-terraform-modules.git?ref=master//modules//routes//natgateway"
+  source                 = "git::https://github.com/ministryofjustice/hmpps-terraform-modules.git//modules/routes/natgateway?ref=master"
   route_table_id         = "${local.route_table_db_ids}"
   destination_cidr_block = "${local.destination_cidr_blocks}"
   nat_gateway_id         = "${local.nat_gateway_ids}"