Fix deprecation warning when importing the ABCs from 'collections'
Fix deprecation warning when importing the ABCs from 'collections'

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