package debian: use /bin/mkdir instead of /usr/bin/mkdir
package debian: use /bin/mkdir instead of /usr/bin/mkdir

Fedora has /usr/bin/mkdir but Debian GNU/Linux and Ubuntu
doesn't have /usr/bin/mkdir.

hiroyuki-sato/groonga,komainu8/groonga,naoa/groonga,redfigure/groonga,naoa/groonga,groonga/groonga,naoa/groonga,groonga/groonga,hiroyuki-sato/groonga,naoa/groonga,kenhys/groonga,cosmo0920/groonga,groonga/groonga,hiroyuki-sato/groonga,kenhys/groonga,redfigure/groonga,groonga/groonga,komainu8/groonga,naoa/groonga,hiroyuki-sato/groonga,komainu8/groonga,cosmo0920/groonga,komainu8/groonga,redfigure/groonga,redfigure/groonga,komainu8/groonga,hiroyuki-sato/groonga,naoa/groonga,kenhys/groonga,cosmo0920/groonga,redfigure/groonga,cosmo0920/groonga,kenhys/groonga,groonga/groonga,kenhys/groonga,redfigure/groonga,hiroyuki-sato/groonga,groonga/groonga,cosmo0920/groonga,komainu8/groonga,komainu8/groonga,redfigure/groonga,naoa/groonga,komainu8/groonga,naoa/groonga,cosmo0920/groonga,groonga/groonga,redfigure/groonga,groonga/groonga,hiroyuki-sato/groonga,kenhys/groonga,hiroyuki-sato/groonga,kenhys/groonga,cosmo0920/groonga,cosmo0920/groonga,kenhys/groonga