Adding python3.8 testing
Adding python3.8 testing

MSeifert04/astropy,astropy/astropy,mhvk/astropy,astropy/astropy,larrybradley/astropy,saimn/astropy,saimn/astropy,mhvk/astropy,pllim/astropy,pllim/astropy,aleksandr-bakanov/astropy,StuartLittlefair/astropy,MSeifert04/astropy,saimn/astropy,StuartLittlefair/astropy,aleksandr-bakanov/astropy,lpsinger/astropy,larrybradley/astropy,lpsinger/astropy,dhomeier/astropy,saimn/astropy,larrybradley/astropy,MSeifert04/astropy,astropy/astropy,mhvk/astropy,mhvk/astropy,mhvk/astropy,stargaser/astropy,lpsinger/astropy,astropy/astropy,StuartLittlefair/astropy,aleksandr-bakanov/astropy,stargaser/astropy,StuartLittlefair/astropy,pllim/astropy,stargaser/astropy,StuartLittlefair/astropy,dhomeier/astropy,larrybradley/astropy,pllim/astropy,astropy/astropy,lpsinger/astropy,pllim/astropy,dhomeier/astropy,lpsinger/astropy,stargaser/astropy,MSeifert04/astropy,dhomeier/astropy,aleksandr-bakanov/astropy,larrybradley/astropy,saimn/astropy,dhomeier/astropy