[CI] remove travis badge

Author: nim65s

README.md

@@ -1,7 +1,6 @@
 # dynamic-graph-tutorial
 
 [![License](https://img.shields.io/badge/License-BSD%202--Clause-orange.svg)](https://opensource.org/licenses/BSD-2-Clause)
-[![Building Status](https://travis-ci.org/stack-of-tasks/dynamic-graph-tutorial.svg?branch=master)](https://travis-ci.org/stack-of-tasks/dynamic-graph-tutorial)
 [![Pipeline status](https://gepgitlab.laas.fr/stack-of-tasks/dynamic-graph-tutorial/badges/master/pipeline.svg)](https://gepgitlab.laas.fr/stack-of-tasks/dynamic-graph-tutorial/commits/master)
 [![Coverage report](https://gepgitlab.laas.fr/stack-of-tasks/dynamic-graph-tutorial/badges/master/coverage.svg?job=doc-coverage)](http://projects.laas.fr/gepetto/doc/stack-of-tasks/dynamic-graph-tutorial/master/coverage/)