Remove Travis badge from README.md

Author: jplatte

README.md

@@ -1,6 +1,5 @@
 # env_logger
 
-[![Build Status](https://travis-ci.org/env-logger-rs/env_logger.svg?branch=master)](https://travis-ci.org/env-logger-rs/env_logger)
 [![Maintenance](https://img.shields.io/badge/maintenance-actively%20maintained-brightgreen.svg)](https://github.com/env-logger-rs/env_logger)
 [![crates.io](https://img.shields.io/crates/v/env_logger.svg)](https://crates.io/crates/env_logger)
 [![Documentation](https://docs.rs/env_logger/badge.svg)](https://docs.rs/env_logger)