Droplet Applescript Touch
You can use Automator to create your droplet. The process of updating a file's time stamp is called touch; this superuser question explains more, How can I “touch” a file from the Mac UI?


Launch Automator.app
Create a new workflow
Add a Run Shell Script action
Set Pass input: to as arguments
Within the script, replace echo with touch
Save your workflow as an application




To learn more about using Automator, see Apple's Mac Basics: Automator.