Revive progress and warning logs (#203)

These got dropped when we pulled in:
https://github.com/google/go-containerregistry/pull/481

Which doesn't log by default, and requires opting in.

cmd/ko/main.go

@@ -16,13 +16,18 @@ package main
 
 import (
 	"log"
+	"os"
 
+	"github.com/google/go-containerregistry/pkg/logs"
 	"github.com/google/ko/pkg/commands"
 
 	"github.com/spf13/cobra"
 )
 
 func main() {
+	logs.Warn.SetOutput(os.Stderr)
+	logs.Progress.SetOutput(os.Stderr)
+
 	// Parent command to which all subcommands are added.
 	cmds := &cobra.Command{
 		Use:   "ko",