update ubuntu version - github pages no longer supports 18.04

Author: KimberleyCook

.github/workflows/cd.yml

@@ -7,7 +7,7 @@ on:
 
 jobs:
   deploy:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
 
@@ -38,4 +38,3 @@ jobs:
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: ./www/public
-