Add go1.21 support (#22)

Author: mstmdev

.github/workflows/go.yml

@@ -11,7 +11,7 @@ jobs:
   build:
     strategy:
       matrix:
-        go: [ '1.18','1.19','1.20' ]
+        go: [ '1.18','1.19','1.20','1.21' ]
         os: [ 'ubuntu-latest', 'windows-latest', 'macos-latest' ]
     runs-on: ${{ matrix.os }}
     steps: