remove outdated travis badge

Author: JuliaSprenger

README.rst

@@ -31,9 +31,6 @@ A project with similar aims but for neuroimaging file formats is `NiBabel`_.
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-.. image:: https://travis-ci.org/NeuralEnsemble/python-neo.png?branch=master
-   :target: https://travis-ci.org/NeuralEnsemble/python-neo
-   :alt: Core Unit Test Status (TravisCI)
 .. image:: https://github.com/NeuralEnsemble/python-neo/actions/workflows/core-test.yml/badge.svg?event=push&branch=master
    :target: https://github.com/NeuralEnsemble/python-neo/actions?query=event%3Apush+branch%3Amaster
    :alt: Core Test Status (Github Actions)