add Go 1.20, 1.19, 1.18 and 1.17 to the build matrix.

Author: shogo82148

.github/workflows/test.yaml

@@ -11,7 +11,13 @@ jobs:
     strategy:
       matrix:
         os: [windows-latest, macos-latest, ubuntu-latest]
-        go: ["1.15", "1.16"]
+        go:
+          - "1.15"
+          - "1.16"
+          - "1.17"
+          - "1.18"
+          - "1.19"
+          - "1.20"
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v2