rename workflow and change README badge

Author: nogates

.github/workflows/main.yml

@@ -1,4 +1,4 @@
-name: Main
+name: Test
 
 on:
  pull_request:

README.md

@@ -1,6 +1,6 @@
 # Zendesk API Client
 
-[![Build Status](https://secure.travis-ci.org/zendesk/zendesk_api_client_rb.svg?branch=master)](http://travis-ci.org/zendesk/zendesk_api_client_rb)
+![Test](https://github.com/zendesk/zendesk_api_client_rb/workflows/Test/badge.svg)
 [![Gem Version](https://badge.fury.io/rb/zendesk_api.svg)](http://badge.fury.io/rb/zendesk_api)
 [![Code Climate](https://codeclimate.com/github/zendesk/zendesk_api_client_rb.svg)](https://codeclimate.com/github/zendesk/zendesk_api_client_rb)