Use --runInBand flag for Jest to improve performance in Circle CI

http://stackoverflow.com/questions/36747251/error-running-jest-on-circleci-npm-test-died-unexpectedly

circle.yml

@@ -24,4 +24,4 @@ test:
   pre:
     - yarn run build
   override:
-    - yarn test
+    - yarn run test-ci

package.json

@@ -20,6 +20,7 @@
     "dev": "sharetribe-scripts start",
     "build": "sharetribe-scripts build",
     "test": "sharetribe-scripts test --env=jsdom",
+    "test-ci": "sharetribe-scripts test --env=jsdom --runInBand",
     "eject": "sharetribe-scripts eject",
     "start": "node server/index.js",
     "dev-server": "npm run build&&nodemon --watch server server/index.js"