Replaced link to .travis.yml in Readme with azure-pipelines.yml

Author: TheSilvus

README.md

@@ -14,7 +14,7 @@ git2 = "0.8"
 ## Rust version requirements
 
 git2-rs works with stable Rust, and typically works with the most recent prior
-stable release as well. Check [.travis.yml](.travis.yml) to see the oldest
+stable release as well. Check [azure-pipelines.yml](azure-pipelines.yml) to see the oldest
 version of Rust known to pass tests.
 
 ## Version of libgit2