changed a message so that it doesn't register as an error according to drdr

collects/teachpack/2htdp/scribblings/image-gen.ss

@@ -101,10 +101,9 @@
 (for-each handle-image expressions)
 (cond
   [(null? mapping)
-   (error 'image-gen "didn't find any images; probably this means that you need to delete .zo files and try again")]
+   (printf "image-gen: didn't find any images; probably this means that you need to delete .zo files and try again\n")]
   [else
-   (printf "\n")])
-
+   (printf "\n")
    (call-with-output-file "image-toc.ss"
      (λ (port)
        (fprintf port "#lang scheme/base\n(provide mapping)\n")
@@ -112,4 +111,4 @@
        (pretty-print
         `(define mapping (list ,@mapping))
         port))
-  #:exists 'truncate)
+     #:exists 'truncate)])