mac-capture: Fix display capture cursor bug

The kCGDisplayStreamShowCursor option used with the dictionary does not
work if you assign @true or @false to it.  After some testing, it needs
to point to the id cast of either kCFBooleanTrue or kCFBooleanFalse in
order for it to work properly.

If it doesn't use either of those values, the display stream seems to
use its internal default, which on 10.8 and 10.9 is visible, and 10.10+
is invisible, which would explain why people on 10.10 couldn't get the
cursor to capture.