Test on both nightly and beta

Author: sfackler

.travis.yml

@@ -1,11 +1,14 @@
 language: rust
+rust:
+- nightly
+- beta
 addons:
   postgresql: 9.3
 script:
 - cargo test
 - cargo doc --no-deps
 after_success:
-- test $TRAVIS_PULL_REQUEST == "false" && test $TRAVIS_BRANCH == "master" && ./.travis/update_docs.sh
+- test $TRAVIS_PULL_REQUEST == "false" && test $TRAVIS_BRANCH == "master" && test $TRAVIS_RUST_VERSION == "nightly" && ./.travis/update_docs.sh
 env:
   global:
     secure: r3ugr11ER3l892nwRNDgpf3PMzZ+hucTGuhGHdatUiMGJ6us9E4inhG+dqvV8UoctMFjaO1tYxVHlwpgxo17Spnc6lopH+MrRHP7H42eEkUZbMEAKiHss/M1w6KocVEKsJdTtaNfN8V7MWAjCDAIL4txTbffBGnIfBhPGWVh09M=