Fixup readme badges, remove travis config (#85)

This change does three things:

1. Removes the travis-ci config file. The project switched to GitHub
   Actions in #76, so I don't believe this file is used any longer.

2. Switches the CI badge from the non-working travis-ci link to a similar
   one for the GitHub Actions test workflow status.

3. Removes the requires.io badge entirely, as the service [shut down] in
   2022.

[shut down]: http://shiningpanda.com/requires-io-clap-de-fin/

Co-authored-by: Dustin Ingram <di@users.noreply.github.com>

README.rst

@@ -1,16 +1,12 @@
 Vladiate
 ========
 
-.. image:: https://travis-ci.org/di/vladiate.svg?branch=master
-    :target: https://travis-ci.org/di/vladiate
+.. image:: https://github.com/di/vladiate/actions/workflows/test.yml/badge.svg?query=branch%3Amaster+event%3Apush
+    :target: https://github.com/di/vladiate/actions/workflows/test.yml?query=branch%3Amaster+event%3Apush
 
 .. image:: https://coveralls.io/repos/di/vladiate/badge.svg?branch=master
     :target: https://coveralls.io/github/di/vladiate
 
-.. image:: https://requires.io/github/di/vladiate/requirements.svg?branch=master
-     :target: https://requires.io/github/di/vladiate/requirements/?branch=master
-     :alt: Requirements Status
-
 Description
 -----------