assign_public_ip was actually added in 1.5

Checked 1.4.5 and this option doesn't exist. Will check/update/pull docs next.

library/cloud/ec2

@@ -170,7 +170,7 @@ options:
     default: null
     aliases: []
   assign_public_ip:
-    version_added: "1.4"
+    version_added: "1.5"
     description:
       - when provisioning within vpc, assign a public IP address. Boto library must be 2.13.0+
     required: false