Fix Mono download link.
Fix Mono download link.

forki/FsCheck,paulyoung/FsCheck,fscheck/FsCheck,ErikSchierboom/FsCheck,fsharp/FsCheck,paulyoung/FsCheck,forki/FsCheck,cloudRoutine/FsCheck,jhamm/FsCheck,sideeffffect/FsCheck,fscheck/FsCheck,cloudRoutine/FsCheck,ploeh/FsCheck