Merge #215

215: add travis to readme r=Dylan-DPC a=Dylan-DPC

Add travis badge to readme

Co-authored-by: Dylan DPC <dylan.dpc@gmail.com>

Author: bors[bot]

README.md

@@ -1,5 +1,6 @@
 [![crates.io](https://img.shields.io/crates/v/cross.svg)](https://crates.io/crates/cross)
 [![crates.io](https://img.shields.io/crates/d/cross.svg)](https://crates.io/crates/cross)
+[![Build Status](https://travis-ci.org/rust-embedded/cross.svg?branch=master)](https://travis-ci.org/rust-embedded/cross) 
 
 # `cross`