modal-backdrop no need z-index anymore

[iamthom]

in .modal-backdrop, z-index need to be removed. https://github.com/TalksLab/metro-bootstrap/blob/master/dist/css/metro-bootstrap.css#L5377

I used it along with bootstrap 3.2 and the modal works again..

[fskreuz]

:+1: This needs to be fixed. Verified on my end.

[NelsonReis]

Unfortunately, we no longer have the time to work on this project. This means that bugs will not be fixed and features will not be added unless someone else does so.

If you're interested in fixing up metro-bootstrap, please reply to this GitHub issue (#65).

Thank you for your support.