Update node.js to 10.15.3 in CI template for Hexo

Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

changelogs/unreleased/58748-update-nodejs-to-10-15-3.yml

+---
+title: Update node.js to 10.15.3 in CI template for Hexo
+merge_request: 25943
+author: Takuya Noguchi
+type: other

lib/gitlab/ci/templates/Pages/Hexo.gitlab-ci.yml

 # Full project: https://gitlab.com/pages/hexo
-image: node:6.10.0
+image: node:10.15.3
 
 pages:
   script:
-  - npm install
-  - ./node_modules/hexo/bin/hexo generate
+  - npm install hexo-cli -g
+  - test -e package.json && npm install
+  - hexo generate
   artifacts:
     paths:
     - public