Fix GCC-7 warning on buffer size

[vvidic]

Warning produced with GCC 7.1.0:

ticket.c: In function ‘process_tickets’:
ticket.c:470:44: warning: ‘%s’ directive output may be truncated writing up to 63 bytes into a region of size 53 [-Wformat-truncation=]
   snprintf(buff, sizeof(buff), "granted to %s",
                                            ^~
ticket.c:470:3: note: ‘snprintf’ output between 12 and 75 bytes into a destination of size 64
   snprintf(buff, sizeof(buff), "granted to %s",
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    site_string(tk->leader));
    ~~~~~~~~~~~~~~~~~~~~~~~~

[dmuhamedagic]

Oh, yes, I missed the extra string. Thanks!