corrected required docs as only boolean is allowed

these complex values were not displayed and would always show the fields as requried

lib/ansible/modules/cloud/amazon/ec2_vpc.py

@@ -24,8 +24,8 @@ version_added: "1.4"
 options:
   cidr_block:
     description:
-      - "The cidr block representing the VPC, e.g. 10.0.0.0/16"
-    required: false, unless state=present
+      - "The cidr block representing the VPC, e.g. 10.0.0.0/16", required when I(state) is 'present'.
+    required: false
   instance_tenancy:
     description:
       - "The supported tenancy options for instances launched into the VPC."

lib/ansible/modules/cloud/amazon/elasticache.py

@@ -68,7 +68,7 @@ options:
   cache_subnet_group:
     description:
       - The subnet group name to associate with. Only use if inside a vpc. Required if inside a vpc
-    required: conditional
+    required: false
     default: None
     version_added: "1.7"
   security_group_ids: