Adding npm sync-backend command to build instruction

.travis.yml

@@ -34,5 +34,4 @@ install:
   - pip install --upgrade pip
   - pip install tox tox-travis
   - rm -rf ~/.nvm && git clone https://github.com/creationix/nvm.git ~/.nvm && (cd ~/.nvm && git checkout `git describe --abbrev=0 --tags`) && source ~/.nvm/nvm.sh && nvm install $TRAVIS_NODE_VERSION
-  - npm install
 script: tox -e $TOX_ENV

run_tests.sh

@@ -7,7 +7,6 @@ rm -f .coverage
 export SUPERSET_CONFIG=tests.superset_test_config
 set -e
 superset/bin/superset db upgrade
-superset/bin/superset db upgrade  # running twice on purpose as a test
 superset/bin/superset version -v
 python setup.py nosetests
 coveralls

superset/assets/js_sync_backend.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+set -e
+cd "$(dirname "$0")"
+npm install
+npm run sync-backend

tox.ini

@@ -32,6 +32,7 @@ commands =
   pip wheel -w {homedir}/.wheelhouse -f {homedir}/.wheelhouse .
   pip install --find-links={homedir}/.wheelhouse --no-index .
   pip install -r dev-reqs.txt
+  {toxinidir}/superset/assets/js_sync_backend.sh
   {toxinidir}/run_tests.sh
 
 [testenv:javascript]