minor touchup, covering other case(s) for "y"

ex13.c

@@ -41,11 +41,13 @@ int main(int argc, char *argv[])
             case 'Y':
                 if (i > 2) {
                     printf("%d: 'Y'\n", i);
+                } else {
+                    printf("%d: 'Y' isn't a vowel this time\n", i);
                 }
                 break;
 
             default:
-                printf("%d: %c is not a vowel\n", i, letter);
+                printf("%d: '%c' is not a vowel\n", i, letter);
         }
     }