Build ruby-3.0.0-preview2

Author: eregon

.github/workflows/build.yml

@@ -11,7 +11,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ ubuntu-16.04, ubuntu-18.04, ubuntu-20.04, macos-latest ]
-        ruby: ["truffleruby-20.3.0"]
+        ruby: ["ruby-3.0.0-preview2"]
     runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v2