When `outputTarget` is a string, disable color

[thw0rted]

Console output uses ANSI color escape sequences (^[40m etc) to prettify the results, but if the user provides a string value for the outputTarget, human-readable output is dumped to a text file. As a rule, text editors / IDEs generally do not support escape sequences in text files, so this output mode is likely to be unusable. Color sequences should only be used when the output target is a TTY (console.log).