fix tslint error

Author: dilin-MS2

src/serialmonitor/serialportctrl.ts

@@ -73,7 +73,7 @@ export class SerialPortCtrl {
  return resolve();
  }
 
- this._currentSerialPort.write("TestingOpen" + '\r\n', (err) => {
+ this._currentSerialPort.write("TestingOpen" + "\r\n", (err) => {
  // TODO: Fix this on the serial port lib: https://github.com/EmergingTechnologyAdvisors/node-serialport/issues/795
  if (err && !(err.message.indexOf("Writing to COM port (GetOverlappedResult): Unknown error code 121") >= 0)) {
  this._outputChannel.appendLine(`[Error] Failed to open the serial port - ${this._currentPort}`);