Update Travis URL

Author: alexcrichton

README.md

@@ -1,6 +1,6 @@
 # backtrace-rs
 
-[![Build Status](https://travis-ci.org/alexcrichton/backtrace-rs.svg?branch=master)](https://travis-ci.org/alexcrichton/backtrace-rs)
+[![Build Status](https://travis-ci.com/alexcrichton/backtrace-rs.svg?branch=master)](https://travis-ci.com/alexcrichton/backtrace-rs)
 [![Build status](https://ci.appveyor.com/api/projects/status/v4l9oj4aqbbgyx44?svg=true)](https://ci.appveyor.com/project/alexcrichton/backtrace-rs)
 
 [Documentation](https://docs.rs/backtrace)