(maint) Bump Leatherman for Xcode 7 fixes
(maint) Bump Leatherman for Xcode 7 fixes

Without the Leatherman fix, pxp-agent will fail to compile on Mac OS X
using Xcode 7 with errors compiling Boost CONCEPT macros.

puppetlabs/pxp-agent,puppetlabs/pxp-agent,puppetlabs/pxp-agent