Fix building on OS X after ca2df01b2d68e4999a5d010f60cbfa61ace079c8

BSD (and Mac) cp uses uppercase -R for recursive functions.  Since
Linux cp supports uppercase -R and -r (they mean the same), switch
to that.

Change-Id: I4888c2083fe313a8bb17be012437b07651a6cca5
Merge pull request #58 from awong-dev/fixmac

Fix building on OS X after ca2df01b2d68e4999a5d010f60cbfa61ace079c8