Remove Travis CI, add GitHub Actions badge

Author: dentarg

.travis.yml

@@ -1,7 +1,7 @@
 # influxdb-ruby
 
 [![Gem Version](https://badge.fury.io/rb/influxdb.svg)](https://badge.fury.io/rb/influxdb)
-[![Build Status](https://travis-ci.org/influxdata/influxdb-ruby.svg?branch=master)](https://travis-ci.org/influxdata/influxdb-ruby)
+[![Build Status](https://github.com/influxdata/influxdb-ruby/workflows/Tests/badge.svg)](https://github.com/influxdata/influxdb-ruby/actions)
 
 The official Ruby client library for [InfluxDB](https://influxdata.com/time-series-platform/influxdb/).
 Maintained by [@toddboom](https://github.com/toddboom) and [@dmke](https://github.com/dmke).