Don't load rake task unless on a supported Ruby

[mlarraz]

The flatui-pro:convert Rake task is the only one in this gem (or bootstrap-sass) that gets loaded directly into the Rails app.

It depends on several scripts in bootstrap-sass that otherwise don't get loaded. One of these uses keyword arguments, a language feature only supported on MRI 2.x.

This wraps the loading of the Rake task in a conditional, so people still on MRI 1.9.3 (or other rubies, like Rubinius) can still use the rest of the gem.

[wingrunr21]

Ok, one thing I would ask is that you add a note to the README stating that the rake task will no longer be available to you if you are running a non-compatible Ruby.

[mlarraz]

I went ahead and added something to the Flat-UI Pro section.

[wingrunr21]

Thanks