Return the correct type from the Monitor#run! function
Return the correct type from the Monitor#run! function

This fixes a crash that happened sometimes while more that one monitor
was running.

ccoenen/wdm,ccoenen/wdm,junseishin/wdm,Maher4Ever/wdm,junseishin/wdm,junseishin/wdm,Maher4Ever/wdm