hterm: Add key code for right Command key.
hterm: Add key code for right Command key.

This is to prevent a console warning when the right Command key is
pressed. To test, press the right Command key on a MacBook Pro and
observe the JavaScript console.

Change-Id: Id044035660a65a05259f996e1658383e09afcf24
Reviewed-on: https://chromium-review.googlesource.com/259461
Reviewed-by: Rob Ginda <4419ac4e35d191308e944202d542b192188656d1@chromium.org>
Tested-by: Rob Ginda <4419ac4e35d191308e944202d542b192188656d1@chromium.org>

chromium/hterm,chromium/hterm,chromium/hterm,chromium/hterm