set maxworkers 2 for frontend tests

scripts/circle-test-frontend.sh

@@ -11,3 +11,4 @@ function exit_if_fail {
 }
 
 exit_if_fail npm run test
+exit_if_fail npm run build

scripts/grunt/options/exec.js

@@ -3,7 +3,7 @@ module.exports = function(config, grunt) {
 
   return {
     tslint: 'node ./node_modules/tslint/lib/tslintCli.js -c tslint.json --project ./tsconfig.json',
-    jest: 'node ./node_modules/jest-cli/bin/jest.js',
+    jest: 'node ./node_modules/jest-cli/bin/jest.js --maxWorkers 2',
     webpack: 'node ./node_modules/webpack/bin/webpack.js --config scripts/webpack/webpack.prod.js',
   };
 };