Improve GitHub Actions workflow (#289)

- Use the strategy.matrix syntax
- Use peaceiris/actions-hugo: https://github.com/peaceiris/actions-hugo

.github/workflows/main.yml

@@ -1,32 +1,23 @@
 name: Build with Hugo
 
-on: [push]
+on: [push, pull_request]
 
 jobs:
-  hugo-latest:
+  build:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        hugo-version:
+          - 'latest'
+          - '0.68.0'
     steps:
-      - uses: actions/checkout@master
+      - uses: actions/checkout@v2
 
-      - name: Install Hugo
-        run: |
-          LATEST_VERSION=`curl --silent "https://api.github.com/repos/gohugoio/hugo/releases/latest" | grep '"tag_name":' | sed -E 's/.*"([^"]+)".*/\1/'`
-          VERSION_NO_PREFIX=`echo $LATEST_VERSION | cut -c 2-`
-          wget "https://github.com/gohugoio/hugo/releases/download/$LATEST_VERSION/hugo_extended_${VERSION_NO_PREFIX}_Linux-64bit.deb" -O /tmp/hugo.deb
-          sudo dpkg -i /tmp/hugo.deb
-
-      - name: Run Hugo
-        working-directory: exampleSite
-        run: hugo --themesDir ../..
-  hugo-minimum:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@master
-
-      - name: Install Hugo
-        run: |
-          wget "https://github.com/gohugoio/hugo/releases/download/v0.68.0/hugo_extended_0.68.0_Linux-64bit.deb" -O /tmp/hugo.deb
-          sudo dpkg -i /tmp/hugo.deb
+      - name: Setup Hugo
+        uses: peaceiris/actions-hugo@v2
+        with:
+          hugo-version: ${{ matrix.hugo-version }}
+          extended: true
 
       - name: Run Hugo
         working-directory: exampleSite