use "go run pkg@version" assuming Go 1.17 or later

Now that Go 1.17 came out four months ago,
we can clean up the go:generate comments.

We don't need to worry about supporting Go 1.16,
as "go generate" only needs to work for the few maintainers.

Fixes #41.

Author: mvdan

code.go

@@ -9,9 +9,7 @@ import (
 
 //go:generate go run gen.go
 //go:generate gofmt -w code_table.go
-//go:generate go get golang.org/x/tools/cmd/stringer
-//go:generate go run golang.org/x/tools/cmd/stringer -type=Code -linecomment
-//go:generate go mod tidy
+//go:generate go run golang.org/x/tools/cmd/[email protected] -type=Code -linecomment
 
 // Code describes an integer reserved in the multicodec table, defined at
 // github.com/multiformats/multicodec.