Update build-jekyll.yml

Author: thetianshuhuang

.github/workflows/build-jekyll.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
-      - uses: actions/cache@v2
+      - uses: actions/cache@v4
         with:
           path: vendor/bundle
           key: ${{ runner.os }}-gems-${{ hashFiles('**/Gemfile') }}