Fix Travis

.travis.yml

@@ -1,6 +1,11 @@
 language: node_js
 sudo: required
 
+cache:
+  yarn: true
+  directories:
+    - node_modules
+
 services:
   - docker
 
@@ -10,6 +15,9 @@ env:
 node_js:
   - "7.4.0"
 
+before_install:
+  - "curl -o- -L https://yarnpkg.com/install.sh | bash"
+
 before_script:
   - "mkdir -p ~/.docker && echo $DOCKER_AUTH > ~/.docker/config.json"
   - "export DISPLAY=:99.0"