add type annotation to work with more recent mono
add type annotation to work with more recent mono

ncave/FSharp.Compiler.Service,dsyme/FSharp.Compiler.Service,cloudRoutine/FSharp.Compiler.Service,cloudRoutine/FSharp.Compiler.Service,ncave/FSharp.Compiler.Service,ncave/FSharp.Compiler.Service,dsyme/FSharp.Compiler.Service,cloudRoutine/FSharp.Compiler.Service,dsyme/FSharp.Compiler.Service