Update bootstrap-select-rails gem, but keep it under 1.13 until we are on Bootstrap 4+

Prompted by the automated !107 (closed) MR, I investigated the effect of updating. Going all the way up to 1.13.x broke the keyboard nav (esp ability to press Enter or Spacebar on the scope picker) and also messed up some styles. I suspect it's because 1.13+ focus on support for Bootstrap 4, and DDR is still on 3.

I was able to remove this line, as this gem (at least this version of it) automatically instantiates the fancy dropdown for an element w/class selectpicker. $('.selectpicker').selectpicker();