async function finish(config, api){
  const {
    tempContractsDir,
    tempArtifactsDir
  } = getTempLocations(config);

  shell.config.silent = true;
  shell.rm('-Rf', tempContractsDir);
  shell.rm('-Rf', tempArtifactsDir);
  shell.config.silent = false;

  if (api) await api.finish();
}
Silently removes temporary folders and calls api.finish to shut server down
@param  {TruffleConfig}     config
@param  {SolidityCoverage}  api
@return {Promise}