attempting at fixing travis-ci build #3

.travis.yml

@@ -9,7 +9,7 @@ matrix:
       osx_image: xcode9.3
       before_install:
         - rustup self uninstall
-        - curl https://sh.rustup.rs -sSf | sh
+        - curl https://sh.rustup.rs -sSf | sh -y
         - rustup install nightly
 
 script: