Fix typo a_dither -> x_dither
@@ -170,7 +170,7 @@ void show_help(void)
" burkes -> Burkes' method\n"
" a_dither -> positionally stable\n"
" arithmetic dither\n"
- " a_dither -> positionally stable\n"
+ " x_dither -> positionally stable\n"
" arithmetic xor based dither\n"
"-f FINDTYPE, --find-largest=FINDTYPE\n"
" choose method for finding the largest\n"
