Fix get_featured (category arg removed).
Fix get_featured (category arg removed).

This commit removes the arg category as it is not needed anymore.

inteligencia-coletiva-lsd/pybossa,Scifabric/pybossa,geotagx/pybossa,harihpr/tweetclickers,inteligencia-coletiva-lsd/pybossa,OpenNewsLabs/pybossa,Scifabric/pybossa,PyBossa/pybossa,CulturePlex/pybossa,jean/pybossa,stefanhahmann/pybossa,harihpr/tweetclickers,CulturePlex/pybossa,proyectos-analizo-info/pybossa-analizo-info,OpenNewsLabs/pybossa,stefanhahmann/pybossa,jean/pybossa,proyectos-analizo-info/pybossa-analizo-info,PyBossa/pybossa,proyectos-analizo-info/pybossa-analizo-info,geotagx/pybossa,CulturePlex/pybossa