Build php 8.0 image (#8)

Author: juulrecognize

.github/workflows/build.yaml

@@ -15,6 +15,7 @@ jobs:
         - '^(7\.2)-apache$'
         - '^(7\.3)-apache$'
         - '^(7\.4)-apache$'
+        - '^(8\.0)-apache$'
     steps:
       - uses: actions/checkout@v1
       - uses: azure/docker-login@v1