Arg parsing fails if URL ends with `]`

autocannon http://localhost\?id=\[1\] results in the help message being shown (if you log argv, it seems that the URL [missing the closing ]] is buried in argv._[0]._[0]).

autocannon http://localhost\?id=\[1\]\&other works as expected though (and logging argv shows that the URL is at argv._[0] as the code expects.