Fix travis.yml.

See http://bettong.net/2014/05/09/how-to-test-rust-on-travis-ci/

.travis.yml

@@ -1,12 +1,13 @@
 env:
   global:
     - secure: GwyxF8F9NKc9M2YypZZMGyIolTf7lDfeKnhhGre28HuzE4e9oIB7dUGjqYrx6uQ/ei++rpd+pjhTFilnX5inS/E+7R7DRvdX00JERWPF+qgiWpxPAoT/iI2RQ+7PKiLcwrzdzQIhSfIse/FikdpkeSY0FJG9/vu/HXNzFxDBPW0=
-before_install:
-  - yes | sudo add-apt-repository ppa:hansjorg/rust
-  - sudo apt-get update
+language: c
 install:
-  - sudo apt-get install rust-nightly
+  - curl -O http://static.rust-lang.org/dist/rust-nightly-x86_64-unknown-linux-gnu.tar.gz
+  - tar xfz rust-nightly-x86_64-unknown-linux-gnu.tar.gz
+  - (cd rust-nightly-x86_64-unknown-linux-gnu/ && sudo ./install.sh)
 script:
+  - rustc --version
   - make
   - make test
   - make bench