Use the new Rust support in Travis-CI

.travis.yml

@@ -1,14 +1,9 @@
-install:
-  - curl -s http://www.rust-lang.org/rustup.sh | sudo sh
-
-script:
-  - cargo build
-  - cargo test
-  - cargo doc
+language: rust
 
 after_success: |
   [ $TRAVIS_BRANCH = master ] &&
   [ $TRAVIS_PULL_REQUEST = false ] &&
+  cargo doc &&
   echo '<meta http-equiv=refresh content=0;url=url/index.html>' > target/doc/index.html &&
   cp github.png target/doc/ &&
   sudo pip install ghp-import &&