`test-network.sh` uses a deprecated bash-specific syntax to do arithmetic. This fails on systems like Ubuntu and Debian that use dash instead of bash for `/bin/sh`. `test-network.sh` should probably use the POSIX `$((arithmetic_expr))` syntax instead. Typical error from the log files: ``` /home/tlyu/src/tor/../chutney/tools/test-network.sh: 302: [: Illegal number: $[n_rounds+1] Completed $[n_rounds+1] of 1 verify rounds. ```