Broken in macOS 10.12.4

[shishkabibal]

Since updating to macOS 10.12.4, changing the screen brightness using the following pattern leads to different/unwanted/unintended behavior:

1. change brightness from command line using "brightness"
2. change brightness again using a function key (F1/F2)

Instead of the 2nd step changing the screen brightness starting from the level set in step 1, macOS 10.12.4 uses the brightness level from before step 1 as its starting point.

[lucasbento]

@kevva and/or @gillstrom: any ideia on how to fix it? I can try to send a PR if I have any idea of what is going on.