Improved ventilation T4 arm

I ran into issues with the standard T4 arms and the recommended 3DR motors overheating (see image - red PLA). The design of ventilation holes in the bottom part of the motor seems to have changed over when the original T4 was designed, so I added a few holes to provide better airflow.
I'm using slightly different motors now, but with the new arms they remain cool, even when I run them at 100% over some time (clamped down on my work bench).