Upgrade seed-fu from 2.3.5 to 2.3.6

Adds Rails 5 support. Working toward #14286 (moved).

Changelog: https://github.com/mbleigh/seed-fu/blob/master/CHANGELOG.md#version-236

cc: @rspeicher

mentioned in issue #14286 (moved)

mentioned in commit 62730e54

Status changed to merged

Milestone changed to %8.10

Mentioned in issue #14286 (moved)