Use POSIX -R instead of -r in copy for better portability

In MacOS, -r will exit with 1 if any broken symlinks are
encountered. -r is "implementation-defined" according to POSIX.
-R is well defined.

cook.sh

@@ -178,7 +178,7 @@ function op {
                 then
                     mkdir "${COOKBOOK_BUILD}"
                 else
-                    cp -rp source "${COOKBOOK_BUILD}"
+                    cp -Rp source "${COOKBOOK_BUILD}"
                 fi
 
                 for patch in *.patch