test: change Travis CI setup

Author: halfzebra

.travis.yml

@@ -15,8 +15,11 @@ before_install:
   - export DISPLAY=':99.0'
   - Xvfb :99 -screen 0 1024x768x24 > /dev/null 2>&1 &
 install:
-  - yarn install
+  - npm install
+  - cd packages/create-elm-app
+  - npm install
   - npm link
+  - cd ..
 script: npm test
 after_success:
   - npm run semantic-release