pkg/build.sh: Follow debian versioning policies

 * The package version number is now in line with the Debian Guidelines:
   "The package management system will break the version number apart at the
   last hyphen in the string (if there is one) to determine the upstream_version
   and debian_revision." - (http://www.debian.org/doc/debian-policy/ch-controlfields.html#s-f-Version)