Update default_value to fix: Protected methods do not respond on ruby 2.0.

https://github.com/FooBarWidget/default_value_for/commit/6f5a7ff4eea5ec446d43fe82deab47a7d77aada4
Available in these git tags: release-3.0.0.1 release-3.0.0 release-2.0.3 release-2.0.2

Came from this PR:
https://github.com/FooBarWidget/default_value_for/pull/29

We'll upgrade to version 3.0.0+ once we get past #488.
Fixes #393