message: src/processor: improve log message
diff: @@ -20,8 +20,8 @@ export default function processor(err: AirbrakeError, cb: Callback): void {
  try {
  frames = ErrorStackParser.parse(err);
  } catch (err) {
  - if (hasConsole) {
  - console.warn('airbrake-js: ErrorStackParser failed:', err.toString());
  + if (hasConsole && err.stack) {
  + console.warn('airbrake-js: cannot parse stack:', err.stack);
  }
  }
  }
  