Replace Travis CI badge with GitHub Actions (#212)

Author: atouchet

README.md

@@ -1,7 +1,7 @@
 ## rust-harfbuzz
 
-[![Build Status](https://travis-ci.org/servo/rust-harfbuzz.svg)](https://travis-ci.org/servo/rust-harfbuzz)
+[![Build Status](https://github.com/servo/rust-harfbuzz/actions/workflows/main.yml/badge.svg)](https://github.com/servo/rust-harfbuzz/actions)
 
-[Documentation](https://docs.rs/harfbuzz-sys/)
+[Documentation](https://docs.rs/harfbuzz-sys)
 
-Bindings to the Harfbuzz text shaping engine
+Bindings to the HarfBuzz text shaping engine.