Update to the newest inherited_resources

The 1.5.0 version of inherited_resources was causing issues with belongs_to associations in a controller.  See the discussion here - https://github.com/activeadmin/activeadmin/pull/3193

Version 1.5.1 was released to fix this issue.  This PR updates AA to require version 1.5.1 or higher of inherited_resources.
Not that I know
On Oct 29, 2014 9:43 PM, "Timo Schilling" <notifications@github.com> wrote:

> In activeadmin.gemspec:
>
> > @@ -20,7 +20,7 @@ Gem::Specification.new do |s|
> >    s.add_dependency 'coffee-rails'
> >    s.add_dependency 'formtastic',          '~> 3.0'
> >    s.add_dependency 'formtastic_i18n'
> > -  s.add_dependency 'inherited_resources', '~> 1.4.1'
> > +  s.add_dependency 'inherited_resources', '>= 1.5.1'
>
> Why not '~> 1.4', '!= 1.5.0', or is there a reason to cat of 1.4?
>
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> <https://github.com/activeadmin/activeadmin/pull/3538/files#r19580531>.
>