Python 3.4 compat: Adapt unit test as error message has changed
Python 3.4 compat: Adapt unit test as error message has changed

liqd/adhocracy3.mercator,fhartwig/adhocracy3.mercator,fhartwig/adhocracy3.mercator,xs2maverick/adhocracy3.mercator,liqd/adhocracy3.mercator,fhartwig/adhocracy3.mercator,liqd/adhocracy3.mercator,xs2maverick/adhocracy3.mercator,xs2maverick/adhocracy3.mercator,liqd/adhocracy3.mercator,xs2maverick/adhocracy3.mercator,fhartwig/adhocracy3.mercator,liqd/adhocracy3.mercator,liqd/adhocracy3.mercator,liqd/adhocracy3.mercator,xs2maverick/adhocracy3.mercator,fhartwig/adhocracy3.mercator,xs2maverick/adhocracy3.mercator,fhartwig/adhocracy3.mercator,fhartwig/adhocracy3.mercator