Added quotation to --keyfile value

based on
https://groups.google.com/forum/#!topic/fsharp-opensource/9hcsDeiFo58
fixed "" to -- keyfile:""

fix based on suggestion by Don syme. This issues was preventing a
successful build.

https://groups.google.com/forum/#!topic/fsharp-opensource/9hcsDeiFo58
Merge pull request #134 from bikal/master

Fixed issue #133