Add missing run command.

No idea what it was tying to build, but it was building something.

.travis.yml

@@ -12,7 +12,7 @@ install:
   - pip install --user -r requirements.txt
   - pip install --user coveralls codeclimate-test-reporter
   - npm install
-  - npm build
+  - npm run build
 
 before_script:
   - python manage.py collectstatic --noinput