Fix doctest example in Dist.Distributor.setDistributorName().
Fix doctest example in Dist.Distributor.setDistributorName().

See https://travis-ci.org/isislovecruft/bridgedb/jobs/16798991#L1591, it
was erroring because it expected the default hashring name for every
hashring which was prepopulated.

wfn/bridgedb,wfn/bridgedb,mmaker/bridgedb,pagea/bridgedb,mmaker/bridgedb,pagea/bridgedb