ENGCOM-1461: [Forwardport] chore: upgrade Node.js to 8 #15033

 - Merge Pull Request #15033 from DanielRuf/magento2:2.3-develop-PR-port-15018
 - Merged commits:
   1. e0ca75b

Author: magento-engcom-team

.travis.yml

@@ -22,7 +22,7 @@ env:
   global:
     - COMPOSER_BIN_DIR=~/bin
     - INTEGRATION_SETS=3
-    - NODE_JS_VERSION=6
+    - NODE_JS_VERSION=8
     - MAGENTO_HOST_NAME="magento2.travis"
   matrix:
     - TEST_SUITE=unit