Add circle ci test for post build

Author: Alex

circle.yml

@@ -105,6 +105,19 @@ jobs:
           environment:
             DEBUG: netlify-plugin-cypress
 
+  'test-postbuild-start':
+    executor: cypress/base-12-14-0
+    steps:
+      # all dependencies were installed in previous job
+      - attach_workspace:
+          at: ~/
+      - run:
+          name: Netlify Build 🏗
+          command: npm run netlify:build
+          working_directory: tests/test-postbuild-start
+          environment:
+            DEBUG: netlify-plugin-cypress
+
   'test-using-chromium':
     executor: cypress/base-12-14-0
     steps: