Only publish docs on nightly

Author: sfackler

.travis.yml

@@ -11,7 +11,7 @@ script:
 - cargo test --features "uuid rustc-serialize time unix_socket serde"
 - cargo doc --no-deps --features "unix_socket"
 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: cZEcWfKI7Pml5og9o1zBMYhbj20Pa22kYVDTDEHqvOoe0kq1cnB5sTH7P0FUgiPq2Ax4B8eQIaC30yvFJ02R7kmTys4aQD98NyCyzdO+dqYi93C9PFYGhl/DKsb4iZ2VP+8LffYSwRGsNSzE9Fj9SFRMIOjHN+UfaVHXaUVjE7Y=