You don't have to restart for the Bash update to take. Just update in the normal way.

sudo apt-get update sudo apt-get dist-upgrade

If you (for whatever nonsensical reason) need to limit that to Bash, you can:

sudo apt-get update sudo apt-get install bash

And again, because of the way this exploit is launched (setting an environment variable before starting a new instance of Bash), you don't need to reboot after you do this.