Upgrade seed-fu from 2.3.5 to 2.3.6

Adds Rails 5 support.

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

Gemfile.lock

@@ -649,9 +649,9 @@ GEM
     sdoc (0.3.20)
       json (>= 1.1.3)
       rdoc (~> 3.10)
-    seed-fu (2.3.5)
-      activerecord (>= 3.1, < 4.3)
-      activesupport (>= 3.1, < 4.3)
+    seed-fu (2.3.6)
+      activerecord (>= 3.1)
+      activesupport (>= 3.1)
     select2-rails (3.5.9.3)
       thor (~> 0.14)
     sentry-raven (1.1.0)