Travis: Test on Rust stable, beta, and 1.28

mbrubeck · mbrubeck · commit 30179f8f6529 · 2018-09-07T13:41:58.000-07:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,5 +1,9 @@
 language: rust
-rust: nightly
+rust:
+  - 1.28.0
+  - nightly
+  - beta
+  - stable
 sudo: false
 env:
     matrix:
