add beta and stable builds to travis

.travis.yml

@@ -4,6 +4,8 @@
 dist: trusty
 language: rust
 rust:
+  - stable
+  - beta
   - nightly
 sudo: required
 
@@ -12,6 +14,8 @@ sudo: required
 
 
 matrix:
+  allow_failures:
+  #  - nightly
   # TODO These are all the build jobs. Adjust as necessary. Comment out what you
   # don't need
   include: