Add all three channels to the sample .travis.yml

diff --git a/src/doc/guide.md b/src/doc/guide.md
index 413705198bd8b8ada5777e7fc2865266325b830e..f54f0dcf2fe3f56cc48647d7508f659972164fe2 100644 (file)
--- a/src/doc/guide.md
+++ b/src/doc/guide.md
@@ -376,7 +376,16 @@ To test your project on Travis CI, here is a sample `.travis.yml` file:
 
 ```
 language: rust
+rust:
+  - stable
+  - beta
+  - nightly
+matrix:
+  allow_failures:
+    - rust: nightly
 ```
 
-Please see the [Travis CI Rust documentation](https://docs.travis-ci.com/user/languages/rust/)
-for more information.
+This will test all three release channels, but any breakage in nightly
+will not fail your overall build. Please see the [Travis CI Rust
+documentation](https://docs.travis-ci.com/user/languages/rust/) for more
+information.