fix helloworld config schema
fix helloworld config schema

'required' keyword must have at least one element:
http://json-schema.org/latest/json-schema-validation.html#anchor61

m4ce/universe,mesosphere/universe,AppliedIS/universe,m4ce/universe,mesosphere/universe-1.7,madanadit/universe,dhilipkumars/universe,NimaVaziri/universe,dhilipkumars/universe,mesosphere/universe,dbtucker/universe,errordeveloper/universe,AppliedIS/universe,nalingarg2/universe,madanadit/universe,mesosphere/universe-1.7,ksivask/universe,AppliedIS/universe,ksivask/universe,errordeveloper/universe,healthagentech/universe,titosand/universe,triforkse/universe,DataDog/universe,aloismayr/universe,elodina/universe,kensipe/universe,neunhoef/universe,concord/universe,niteshch207/universe,aloismayr/universe,kensipe/universe,drewkerrigan/universe,mwl/universe,nalingarg2/universe,errordeveloper/universe,niteshch207/universe,ksivask/universe,kensipe/universe,aloismayr/universe,BuoyantIO/universe,socialvibe/universe,DataDog/universe,madanadit/universe,drewkerrigan/universe,neunhoef/universe,NimaVaziri/universe,BuoyantIO/universe,ContainerSolutions/universe,NimaVaziri/universe,dhilipkumars/universe,concord/universe,dmitrypekar/universe,elodina/universe,yuchaoran2011/universe,yuchaoran2011/universe,dmitrypekar/universe,Capgemini/universe,dbtucker/universe,titosand/universe,BuoyantIO/universe,Capgemini/universe,niteshch207/universe,healthagentech/universe,triforkse/universe,socialvibe/universe,ContainerSolutions/universe,mwl/universe,dbtucker/universe,titosand/universe,yuchaoran2011/universe