TASK: Adjust yarn version for travisci

Author: markusguenther

.travis.yml

@@ -6,6 +6,6 @@ cache:
 node_js:
   - "node"
 before_install:
-  - curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version v1.9.4
+  - curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version 1.9.4
   - export PATH="$HOME/.yarn/bin:$PATH"
   - yarn global add babel-cli