message: Use <anonymous> file by default.
diff: @@ -43,7 +43,7 @@ export default function processor(err: AirbrakeError, cb: Callback): void {
  for (let frame of frames) {
  backtrace.push({
  function: frame.functionName || '',
  - file: frame.fileName || '',
  + file: frame.fileName || '<anonymous>',
  line: frame.lineNumber || 0,
  column: frame.columnNumber || 0,
  });
  @@ -53,7 +53,7 @@ export default function processor(err: AirbrakeError, cb: Callback): void {
  if (backtrace.length === 0 && err.fileName && err.lineNumber) {
  backtrace.push({
  function: err.functionName || '',
  - file: err.fileName || '',
  + file: err.fileName || '<anonymous>',
  line: err.lineNumber || 0,
  column: err.columnNumber || 0,
  });
  