Fixed typo.

format.c

@@ -93,7 +93,7 @@ static xs_str *format_line(const char *line, xs_list **attach)
             "\\*\\*?\\*?[^\\*]+\\*?\\*?\\*"     "|"
             "!\\[[^]]+\\]\\([^\\)]+\\)"         "|"
             "\\[[^]]+\\]\\([^\\)]+\\)"          "|"
-            "[a-z]+?:/" "/[^[:space:]]+"
+            "[a-z]+:/" "/[^[:space:]]+"
         ")");
     int n = 0;