Automatically pick go version in GitHub workflow

Author: muesli

.github/workflows/build.yml

@@ -5,7 +5,7 @@ jobs:
   build:
     strategy:
       matrix:
-        go-version: [1.12.x, 1.13.x, 1.14.x, 1.15.x]
+        go-version: [~1.12, ^1]
         os: [ubuntu-latest, macos-latest, windows-latest]
     runs-on: ${{ matrix.os }}
     env: