travis: force install extension deps.

Author: paulirish

.travis.yml

@@ -10,14 +10,14 @@ cache:
    directories:
      - node_modules
      - chrome-linux
-     - extension/node_modules
+     - lighthouse-extension/node_modules
 before_script:
+  - npm --prefix ./lighthouse-extension install ./lighthouse-extension
   - export DISPLAY=:99.0
   - export LIGHTHOUSE_CHROMIUM_PATH="$(pwd)/chrome-linux/chrome"
   - sh -e /etc/init.d/xvfb start
   - ./lighthouse-core/scripts/download-chrome.sh
   - start-stop-daemon --start --background --exec $(pwd)/lighthouse-core/scripts/launch-chrome.sh
-  - sleep 5
 script:
   - if [[ $(node -v) =~ ^v4.* ]]; then export __node_harmony=--harmony; fi
   - npm run lint