Show the host for the iframe link

Instead of showing only: Click to visit embedded content

An embedded link now displays with the domain it's linking to: Embedded
content at example.com

This hopefully breaks up the links a bit so it'e easier to distinguish
between a bunch of them in a row (as long as they are on different
domains).

spec/models/nodes_spec.cr

@@ -1,6 +1,14 @@
 require "../spec_helper"
 
 module Nodes
+  describe IFrame do
+    it "returns embedded url with subdomains" do
+      iframe = IFrame.new(href: "https://dev.example.com/page")
+
+      iframe.domain.should eq("dev.example.com")
+    end
+  end
+
   describe Image do
     it "adjusts the width and height proportionally" do
       image = Image.new(src: "image.png", originalWidth: 1000, originalHeight: 603)