fix extra parameters params for the links

[kevinhughes27]

I'm using kaminari with sinatra on a project and I need to use extra parameters with the pagination links. The kaminari documentation describes this here https://github.com/kaminari/kaminari#extra-parameters-params-for-the-links. Unfortunately this doesn't seem to be working with the sinatra gem in my project (I didn't test a vanilla application).

I did some digging and this patch fixed the problem for me. I'm not sure it is the best solution since merging the idea of current_params and extra_params might be confusing but this was the fix with the least impact on the existing code so I thought I would start here. I'm happy to go further with some guidance from a maintainer.

Also the tests crashed on my machine so hopefully travis still runs.

[kevinhughes27]

Travis is failing with the same error I see locally :disappointed:

[kevinhughes27]

Just noticed I am still on my branch for this, any interest in getting this merged?