Cleanup Continuous Integration (#384)

* Remove "stale" workflow. It was a nice idea, but deactivated for quite some time anyway

* Remove TravisCI

Author: andygrunwald

.github/workflows/stale.yml

@@ -1,7 +1,7 @@
 # go-jira
 
 [![GoDoc](https://godoc.org/github.com/andygrunwald/go-jira?status.svg)](https://godoc.org/github.com/andygrunwald/go-jira)
-[![Build Status](https://travis-ci.org/andygrunwald/go-jira.svg?branch=master)](https://travis-ci.org/andygrunwald/go-jira)
+[![Build Status](https://github.com/andygrunwald/go-jira/actions/workflows/testing.yml/badge.svg)](https://github.com/andygrunwald/go-jira/actions/workflows/testing.yml)
 [![Go Report Card](https://goreportcard.com/badge/github.com/andygrunwald/go-jira)](https://goreportcard.com/report/github.com/andygrunwald/go-jira)
 
 [Go](https://golang.org/) client library for [Atlassian Jira](https://www.atlassian.com/software/jira).