drop go1.15 support

Author: techknowlogick

.github/workflows/ci.yml

@@ -13,18 +13,18 @@ jobs:
   test:
     strategy:
       matrix:
-        go-version: [ 1.15.x, 1.16.x, 1.17.x, 1.18.x, 1.19.x, 1.20.x, 1.21.x ]
+        go-version: [ 1.16.x, 1.17.x, 1.18.x, 1.19.x, 1.20.x, 1.21.x ]
         os: [ubuntu-latest, macos-latest, windows-latest]
     runs-on: ${{ matrix.os }}
     steps:
     - name: Install Go
-      uses: actions/setup-go@v2
+      uses: actions/setup-go@v4
       with:
         go-version: ${{ matrix.go-version }}
     - name: Checkout code
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
     - name: Restore cache
-      uses: actions/cache@v2
+      uses: actions/cache@v3
       with:
         path: ~/go/pkg/mod
         key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}