Remove travis references

Travis has not been used by AlarmDecoder in many years and I merged a
lot of GitHub Actions workflows in #79. Therefore, this PR removes any
remaining TravisCI remnants from the repository.

Author: ajschmidt8

.travis.yml

@@ -11,8 +11,8 @@
 AlarmDecoder
 ============
 
-.. image:: https://travis-ci.org/nutechsoftware/alarmdecoder.svg?branch=master
-    :target: https://travis-ci.org/nutechsoftware/alarmdecoder
+.. image:: https://github.com/nutechsoftware/alarmdecoder/actions/workflows/merge.yaml/badge.svg
+    :target: https://github.com/nutechsoftware/alarmdecoder/actions/workflows/merge.yaml
 
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