Add Centos8

I'm sure this can be done with a container matrix but figuring that out
is left for another day.

.github/workflows/build.yml

@@ -33,7 +33,7 @@ jobs:
           repository: ${{ env.GITHUB_REPOSITORY }}
           ref: ${{ env.GITHUB_HEAD_REF }}
 
-      - name: Install redis-server
+      - name: Install dependencies
         run: |
           yum -y install http://rpms.remirepo.net/enterprise/remi-release-7.rpm
           yum -y --enablerepo=remi install redis
@@ -45,6 +45,29 @@ jobs:
       - name: Run tests
         run: $GITHUB_WORKSPACE/test.sh
 
+  centos8:
+    runs-on: ubuntu-latest
+    container: centos:8
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+        with:
+          repository: ${{ env.GITHUB_REPOSITORY }}
+          ref: ${{ env.GITHUB_HEAD_REF }}
+
+      - name: Install dependencies
+        run: |
+          dnf -y install https://rpms.remirepo.net/enterprise/remi-release-8.rpm
+          dnf -y module install redis:remi-6.0
+          dnf -y group install "Development Tools"
+          dnf -y install openssl-devel
+
+      - name: Build hiredis
+        run: USE_SSL=1 make
+
+      - name: Run tests
+        run: $GITHUB_WORKSPACE/test.sh
+
   macos:
     runs-on: macos-latest
     steps: