Further fix help screen formatting

[tkchia]

Hello @jart,

This patch fixes a remaining minor problem in the formatting of the help screen — following up on @ghaerr's patch (https://github.com/jart/blink/pull/3):

00009a21          50                    push    %rax                            
00009a22          54                    push    %rsp                            
000                                                                             
000 ╔════════════════════════════════════════════════════════════════════╗      
000 ║                                                                    ║      
000 ║  BLINK v1.o                 https://justine.lol/blinkenlights/  ║ 4f8(%rip
000 ║                                                                    ║      
000 ║  KEYBOARD SHORTCUTS                 CLI FLAGS                      ║      
000 ║                                                                    ║      
000 ║  ctrl-c  interrupt                  -t       tui mode              ║      
000 ║  s       step                       -r       real mode             ║     
...

The problem was that the top line (BLINK v1.o etc.) contains ESC [ ... control sequences, so directly laying it out with the format string "...%-*s..." does not quite work, and causes the number of trailing spaces to be calculated wrong.

I will send you the required copyright assignment e-mail for this project soon.

Thank you!