Remove warning for double semicolons ;;

[divyekapoor]

warning: unnecessary trailing semicolon
  --> src/commands/monitor.rs:26:15
   |
26 |             );;
   |               ^ help: remove this semicolon
   |
   = note: `#[warn(redundant_semicolons)]` on by default

warning: `beanstalkd-cli` (bin "beanstalkd-cli") generated 1 warning
    Finished dev [unoptimized + debuginfo] target(s) in 45.32s