Update travis.yml - use rustup

.travis.yml

-language: rust
-rust:
-  - nightly
+language: generic
 sudo: required
 install:
+  - curl https://sh.rustup.rs -sSf > rustup; chmod +x rustup; ./rustup --default-toolchain nightly -y
   - ./setup.sh
 script: ./jenkins.sh
 notifications: