Use Go 1.17 in CI

Also drop tests for 1.13 and 1.14, these are no longer supported
upstream. Keep 1.12 though as this is the mimimum supported version for
gops.

Author: tklauser

.github/workflows/test.yml

@@ -12,7 +12,8 @@ jobs:
   test:
     strategy:
       matrix:
-        go-version: [1.12, 1.13, 1.14, 1.15, 1.16]
+        # Minimum supported version (1.12) and the latest few versions
+        go-version: [1.12, 1.15, 1.16, 1.17]
         platform: [ubuntu-latest, macos-latest, windows-latest]
     runs-on: ${{ matrix.platform }}
 
@@ -26,11 +27,11 @@ jobs:
       uses: actions/checkout@v2
 
     - name: Check formatting
-      if: matrix.go-version == '1.16' && matrix.platform == 'ubuntu-latest'
+      if: matrix.go-version == '1.17' && matrix.platform == 'ubuntu-latest'
       run: diff -u <(echo -n) <(go fmt $(go list ./...))
 
     - name: Check module vendoring
-      if: matrix.go-version == '1.16' && matrix.platform == 'ubuntu-latest'
+      if: matrix.go-version == '1.17' && matrix.platform == 'ubuntu-latest'
       run: |
         go mod tidy
         go mod vendor