Simplify polyfills.

src/polyfills.ts

@@ -1,11 +1,3 @@
 import 'core-js/es6';
 import 'core-js/es7/reflect';
-require('zone.js/dist/zone');
+import 'zone.js/dist/zone';
-
-if (process.env.ENV === 'production') {
-  // Production
-} else {
-  // Development and test
-  Error['stackTraceLimit'] = Infinity;
-  require('zone.js/dist/long-stack-trace-zone');
-}