Support exec plugin on Windows

api/internal/plugins/execplugin/execplugin.go

@@ -9,6 +9,7 @@ import (
 	"io/ioutil"
 	"os"
 	"os/exec"
+	"runtime"
 	"strings"
 
 	"github.com/google/shlex"
@@ -50,7 +51,9 @@ func (p *ExecPlugin) ErrIfNotExecutable() error {
 	if err != nil {
 		return err
 	}
-	if f.Mode()&0111 == 0000 {
+	// In Windows, it is not possible to determine whether a
+	// file is executable through file mode.
+	if f.Mode()&0111 == 0000 && runtime.GOOS != "windows" {
 		return fmt.Errorf("unexecutable plugin at: %s", p.path)
 	}
 	return nil