The get_temp() code will stop reporting the last temperature of the
heater if there hasn't been any recent temperature updates. However,
on a full mcu communication loss this can cause the verify_heater code
to report a heating error prior to the mcu code reporting the
communication failure. Increase the heater timeout from 5 to 7
seconds to make it more likely the mcu failure is reported first.
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>