Avoid giving out bridges that suffer from #28912

Bridges running 0.3.4.x before 0.3.4.10 suffer from legacy/trac#28912 (moved), where you basically can't bootstrap from them unless they have other people fetching directory information from them at the same time as you try. Same with 0.3.5.x before 0.3.5.7 I think.

Now that 0.3.4.10 is out, and 0.3.5.7 are out, hopefully bridges will upgrade. But for the ones that don't, we might be wise in bridgedb to decline to give them out.

I wonder what fraction of bridges this affects currently? I cc irl and karsten to find out.