runScript method
Runs a script from the scripts map if it exists.
Implementation
Future<int> runScript(String script, {String extra = ''}) async {
final preScript = lookup('pre$script');
if (preScript != null) await _runScript('pre$script');
final exitCode = _runScript(script, extra: extra);
final postScript = lookup('post$script');
if (postScript != null) await _runScript('post$script');
return exitCode;
}