remove travis CI. it is replaced by github actions for us.

Author: aldas

.travis.yml

@@ -3,7 +3,6 @@
 [![Latest Version](https://img.shields.io/packagist/v/aldas/modbus-tcp-client.svg)](https://packagist.org/packages/aldas/modbus-tcp-client)
 [![Packagist](https://img.shields.io/packagist/dm/aldas/modbus-tcp-client.svg)](https://packagist.org/packages/aldas/modbus-tcp-client)
 [![Software License](https://img.shields.io/packagist/l/aldas/modbus-tcp-client.svg)](LICENSE)
-[![Build Status](https://travis-ci.org/aldas/modbus-tcp-client.svg?branch=master)](https://travis-ci.org/aldas/modbus-tcp-client)
 [![codecov](https://codecov.io/gh/aldas/modbus-tcp-client/branch/master/graph/badge.svg)](https://codecov.io/gh/aldas/modbus-tcp-client)
 
 * Modbus TCP/IP specification: http://www.modbus.org/specs.php