func Update(deps dep.DependencyMap, name string, branch string) {
	util.Print(colors.Blue("Updating:"))
	d, ok := deps.Map[name]
	if !ok {
		util.Fatal(colors.Red("Dependency Name '" + name + "' not found in deps.json"))
	}
	oldVersion := d.Version
	d.Version = branch
	pwd := util.Pwd()
	util.Cd(d.Path())
	d.VCS.Checkout(d)
	d.VCS.Update(d)
	v, err := d.VCS.LastCommit(d, branch)
	if err != nil {
		util.Fatal(err)
	}
	d.Version = v
	util.PrintIndent(colors.Blue(name) + " (" + oldVersion + " --> " + d.Version + ")")
	util.Cd(pwd)
	deps.Map[name] = d
	deps.Write()
	install.Install(deps)
}
Update rewrites Dependency name in deps.json to use the last commit in branch as version
package update
import (
	"github.com/vube/depman/colors"
	"github.com/vube/depman/dep"
	"github.com/vube/depman/install"
	"github.com/vube/depman/util"
)