fixes for camo images

lib/camo/image.ex

@@ -1,10 +1,18 @@
 defmodule Camo.Image do
   def image_url(input) do
-    %{host: host} = URI.parse(input)
+    uri = URI.parse(input)
 
-    if !host or String.ends_with?(host, cdn_host()) or is_nil(camo_key()) do
+    cond do
+      is_nil(uri.host) ->
+        ""
+
+      is_nil(camo_key()) ->
         input
-    else
+
+      uri.host in [cdn_host(), camo_host()] ->
+        URI.to_string(update_in(uri.scheme, fn _ -> "https" end))
+
+      true ->
         camo_digest = :crypto.hmac(:sha, camo_key(), input) |> Base.encode16(case: :lower)
 
         camo_uri = %URI{