Log Message:
p5-Future: update to 0.37.

0.37    2017/11/28 15:39:22
        [CHANGES]
         * Finally got around to removing the old Makefile.PL

        [BUGFIXES]
         * Fix for convergent futures that lose strong references during
           cancellation (RT120468)
         * ->without_cancel shouldn't retain the originating future after
           completion (RT122920)

0.36    2017/11/27 22:04:52
        [CHANGES]
         * Added ->retain method (RT123711)
         * Fixed some typoes in docs (RT118309)
         * Added ->state method (RT120759)

        [BUGFIXES]
         * Ensure that ->without_cancel still strongly holds a reference to
           its parent future (RT122920)