Correct span in disambiguate_location for Oxfordshire

Related to #508
Specify town in Oxfordshire disambiguate_location

Part of #508

This seems like a bit of a misuse of this feature, mostly because I'm
specifying a county in a parameter called town, but it appears to fix
the immediate problem of not being able to find streets in oxfordshire.
Merge branch 'master' into oxfordshire-usability-recommendations