update ci and netlify settings

workflows: remove version 2.4 and add 3.0.x to github ci
netlify: bump RUBY_VERSION to 2.7 since jekyll 4 won't work with
ruby <= 2.6

.github/workflows/ci.yml

@@ -8,11 +8,11 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [ '2.4', '2.5', '2.6', '2.7' ]
+        ruby: [ '2.5', '2.6', '2.7', '3.0.1' ]
     name: Ruby ${{ matrix.ruby }}
     steps:
       - uses: actions/checkout@v2
-      - uses: actions/setup-ruby@v1
+      - uses: ruby/setup-ruby@v1
         with:
           ruby-version: ${{ matrix.ruby }}
       - name: install bundler

netlify.toml

@@ -3,7 +3,7 @@
   command = "jekyll build --trace --limit-posts 10"
 
 [build.environment]
-  RUBY_VERSION = "2.6"
+  RUBY_VERSION = "2.7"
 
 [build.processing]
   skip_processing = true