Update sbt-pgp version to v0.8.2

because of sbt-pgp v0.7 is not for sbt-0.13.x

    [warn] 	::::::::::::::::::::::::::::::::::::::::::::::
    [warn] 	::          UNRESOLVED DEPENDENCIES         ::
    [warn] 	::::::::::::::::::::::::::::::::::::::::::::::
    [warn] 	:: com.typesafe.sbt#sbt-pgp;0.7: not found
    [warn] 	::::::::::::::::::::::::::::::::::::::::::::::
    [warn] 
    [warn] 	Note: Some unresolved dependencies have extra attributes.  Check that these dependencies exist with the requested attributes.
    [warn] 		com.typesafe.sbt:sbt-pgp:0.7 (sbtVersion=0.13, scalaVersion=2.10)