disk_limiter: increase journal cap to 85% of available space
disk_limiter: increase journal cap to 85% of available space

Allow for bigger journals now that they can be written to faster.

Issue: DESKTOP-3800

keybase/kbfs,keybase/kbfs,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client