Re-add `old-locale` dependency

it's still needed otherwise compilation fails
(it got removed in 7172d7223e339bf2a5e15c68b26864a638cc2523)
Minor version bump to 0.8.1.0

...because 0dac7f3611546f424929d24e4d0899e8f430a841
adds a new instance to an exposed type.