Fix versioning in leiningen-2.4.2.ebuild

Currently, ${LEIN_VERSION} in
https://raw.githubusercontent.com/technomancy/leiningen/2.4.2/bin/lein-pkg
is "2.4.1".  Temporarily switch to a personally hosted copy of the
script w/ ${LEIN_VERSION} set to 2.4.2.  Maybe switch to a largely
unchanging lein-pkg script and change the ${LEIN_VERSION} assignment at
merge time?