Add an option to configure the class used to wrap the nested fields. (brought up in issue #178)

My solution was to use the `html_options` parameter of #link_to_remove_association.
If it contains a `wrapper_class` key, it saves that key in the link's data-wrapper-class attribute,
and then uses it in the JS, when trying to remove an item.
Merge pull request #180 from yoavmatchulsky/nested-fields

Add an option to configure the class used to wrap the nested fields. (br...
For the moment remove rbx from travis.

See https://github.com/travis-ci/travis-ci/issues/1641
for more info:

On branch fix_travix_rbx I tried the following:

- rbx-19mode is replaced by rbx
- added missing gems???

But I did not get it to work. So for now just 
disable it.
Use 'rbx' on Travis.
Removed Gemfile.lock.
Use rbx-2.2.1 because RVM still isn't updated.
Added gems for platforms :rbx.
Removed gemfiles/Gemfile.rails-3.2.13.lock.
Added rbx-developer_tools dep for coverage.
Added rubysl-test-unit.
Added platforms :rbx for gemfiles/Gemfile.rails-3.2.13.
Merge pull request #181 from brixen/master

Changes to pass tests on Travis with Rubinius
Version bump to 1.2.4
Ignore `Gemfile.lock`.

It is not good practice to check in `Gemfile.lock`
for a gem. The only use of `Gemfile.lock` is for a
gem developer _or_ an automatic build/continuous
integration. And since travis-ci builds for different
platforms, a single `Gemfile.lock` actually works
counterproductive.
Regenerate gemspec for version 1.2.4
Fix dependencies: they should be for development only.
Version bump to 1.2.5
Regenerate gemspec for version 1.2.5
Update History.

I should do this more often. Doh.