Easy way to get the keys in a map in alphabetical order

In Go, what's the easiest way to get the keys in a map sorted alphabetically? This is the shortest way I can do it:

package main

import "container/vector"
import "fmt"
import "sort"

func main() {
    m := map[string]string {"b":"15", "z":"123123", "x":"sdf", "a":"12"}
    var keys vector.StringVector;
    for k,_ := range ( m ) {
            keys.Push(k)
    }
    sort.Sort( &keys )
    fmt.Printf("%v\n", keys)
}