message: Log objects as JSON in the FileLogWriter
diff: @@ -11,8 +11,11 @@ export class FileLogWriter implements LogWriter {
  write(level: Level, msg: string, ...opts: any[]): void {
  fs.writeSync(this._fhandle, Buffer.from(msg));
  + fs.writeSync(this._fhandle, Buffer.from(' '));
  - fs.writeSync(this._fhandle, Buffer.from(opts.join(', ')));
  + const strOpts = opts.map(opt => typeof opt === 'string' ? opt : JSON.stringify(opt, null, 4));
  +
  + fs.writeSync(this._fhandle, Buffer.from(strOpts.join(', ')));
  fs.writeSync(this._fhandle, Buffer.from('\n'));
  }
  }
  