Switch to my own images, with dependencies satisfied

Necessary PHP modules, as well as Composer, are provided in the new images: https://git.ethitter.com/docker/images/container_registry.

camo-image-proxy.php

@@ -12,4 +12,4 @@
  * @package         Camo_Image_Proxy
  */
 
-// Your code starts here.
+namespace Camo_Image_Proxy;