nlopt: Update external version to get a `.gitignore` fix
nlopt: Update external version to get a `.gitignore` fix

This makes `git status` in the nlopt source tree report a clean tree by
ignoring an executable that appears in its source tree when building
with `octave` installed.

sheim/drake,billhoffman/drake,sheim/drake,billhoffman/drake,sheim/drake,sheim/drake,billhoffman/drake,sheim/drake,sheim/drake,sheim/drake,billhoffman/drake,billhoffman/drake,billhoffman/drake,billhoffman/drake,billhoffman/drake,sheim/drake