Remove Travis CI Badge (Gallopsled#2220)

We don't use Travis CI anymore.

Closes Gallopsled#1740

Author: peace-maker

.travis.yml

@@ -3,7 +3,6 @@
 
 [![PyPI](https://img.shields.io/pypi/v/pwntools?style=flat)](https://pypi.python.org/pypi/pwntools/)
 [![Docs](https://readthedocs.org/projects/pwntools/badge/?version=stable)](https://docs.pwntools.com/)
-[![Travis](https://img.shields.io/travis/Gallopsled/pwntools/dev?logo=Travis)](https://travis-ci.org/Gallopsled/pwntools)
 [![GitHub Workflow Status (dev)](https://img.shields.io/github/actions/workflow/status/Gallopsled/pwntools/ci.yml?branch=dev&logo=GitHub)](https://github.com/Gallopsled/pwntools/actions/workflows/ci.yml?query=branch%3Adev)
 [![Coveralls](https://img.shields.io/coveralls/github/Gallopsled/pwntools/dev?logo=coveralls)](https://coveralls.io/github/Gallopsled/pwntools?branch=dev)
 [![MIT License](https://img.shields.io/badge/license-MIT-blue.svg?style=flat)](http://choosealicense.com/licenses/mit/)