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

@@ -11,3 +11,5 @@
  *
  * @package         Camo_Image_Proxy
  */
+
+namespace Camo_Image_Proxy;