Add CI build on beta toolchain
diff --git a/.travis.yml b/.travis.yml
index 74f438d..273a6c4 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,6 +1,8 @@
 language: rust
 
-rust: nightly
+rust:
+  - nightly
+  - beta
 
 os:
   - linux
@@ -13,6 +15,7 @@
 matrix:
   include:
     - name: Buck
+      rust: nightly
       before_install:
         - sudo apt-get install -y openjdk-8-jdk
         - export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64