frontier_client: bump version to 2.8.7

Request:
  https://hypernews.cern.ch/HyperNews/CMS/get/ext-pkg-mgmt/364.html

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>
Merge pull request #107 from davidlt/IB/CMSSW_6_2_X/stable

frontier_client: bump version to 2.8.7