upgrade klayout to 0.25.8
This is a bug-fix release.
Changelog can be found at https://www.klayout.de/development.html
Test Plan: As before, open a few GDS files (kB to GB in size) and browse the layout. Open Help->About and check it ruby/python bindings are present in the `Build options'.
Reviewers: Triage Team, DataDrake
Reviewed By: Triage Team, DataDrake
Differential Revision: https://dev.getsol.us/D5941