Using yarn instead of npm install (#3120)

.travis.yml

@@ -10,7 +10,7 @@ cache:
 env:
   global:
     - TRAVIS_CACHE=$HOME/.travis_cache/
-    - TRAVIS_NODE_VERSION="6.10.2"
+    - TRAVIS_NODE_VERSION="7.10.0"
   matrix:
     - TOX_ENV=javascript
     - TOX_ENV=pylint
@@ -19,7 +19,7 @@ env:
     - TOX_ENV=py27-mysql
     - TOX_ENV=py27-sqlite
 before_install:
-  - npm install -g npm@'>=4.5.0'
+  - npm install -g npm@'>=5.0.3'
 before_script:
   - mysql -e 'drop database if exists superset; create database superset DEFAULT CHARACTER SET utf8 COLLATE utf8_unicode_ci' -u root
   - mysql -u root -e "CREATE USER 'mysqluser'@'localhost' IDENTIFIED BY 'mysqluserpassword';"

superset/assets/js_build.sh

@@ -3,7 +3,8 @@ set -e
 cd "$(dirname "$0")"
 npm --version
 node --version
-npm install
+npm install -g yarn
+yarn
 npm run sync-backend
 npm run lint
 npm run test