fix(schema.js): fix $ref not being resolved when nested deeper than once within an object

A $ref is not correctly resolved when nested within objects deeper than depth 2. Go recursively over
any object properties that are themselves objects to look for a $ref.

fix #155

Author: matthias-pichler

lib/schema.js

@@ -125,6 +125,10 @@ var processFurther = Promise.method(function(val, key, $id){
               }
             });
           });
+        } else {
+          //type is object but property does not contain a $ref
+          // go recursively down to check for a $ref
+          return processFurther(propertyValue, propertyKey, base$id);
         }
       });