Fix './mach clean-nightlies --keep 3' not keeping anything.
Fix './mach clean-nightlies --keep 3' not keeping anything.

dati91/servo,mattnenterprise/servo,DominoTree/servo,thiagopnts/servo,nnethercote/servo,notriddle/servo,canaltinova/servo,dsandeephegde/servo,fiji-flo/servo,emilio/servo,notriddle/servo,upsuper/servo,notriddle/servo,splav/servo,anthgur/servo,DominoTree/servo,splav/servo,jimberlage/servo,notriddle/servo,mbrubeck/servo,fiji-flo/servo,KiChjang/servo,mattnenterprise/servo,jimberlage/servo,saneyuki/servo,DominoTree/servo,paulrouget/servo,thiagopnts/servo,nnethercote/servo,KiChjang/servo,emilio/servo,eddyb/servo,upsuper/servo,peterjoel/servo,emilio/servo,KiChjang/servo,eddyb/servo,KiChjang/servo,upsuper/servo,dsandeephegde/servo,CJ8664/servo,upsuper/servo,thiagopnts/servo,paulrouget/servo,emilio/servo,saneyuki/servo,saneyuki/servo,dati91/servo,larsbergstrom/servo,notriddle/servo,SimonSapin/servo,avadacatavra/servo,emilio/servo,dati91/servo,sadmansk/servo,splav/servo,avadacatavra/servo,paulrouget/servo,avadacatavra/servo,sadmansk/servo,larsbergstrom/servo,eddyb/servo,thiagopnts/servo,upsuper/servo,anthgur/servo,anthgur/servo,splav/servo,fiji-flo/servo,DominoTree/servo,szeged/servo,ConnorGBrewster/servo,larsbergstrom/servo,DominoTree/servo,ConnorGBrewster/servo,avadacatavra/servo,larsbergstrom/servo,peterjoel/servo,nnethercote/servo,saneyuki/servo,nnethercote/servo,nnethercote/servo,DominoTree/servo,saneyuki/servo,nnethercote/servo,SimonSapin/servo,splav/servo,SimonSapin/servo,splav/servo,peterjoel/servo,mbrubeck/servo,upsuper/servo,mbrubeck/servo,eddyb/servo,paulrouget/servo,sadmansk/servo,paulrouget/servo,fiji-flo/servo,szeged/servo,canaltinova/servo,eddyb/servo,canaltinova/servo,larsbergstrom/servo,pyfisch/servo,jimberlage/servo,rnestler/servo,KiChjang/servo,notriddle/servo,rnestler/servo,dsandeephegde/servo,szeged/servo,paulrouget/servo,larsbergstrom/servo,dati91/servo,larsbergstrom/servo,thiagopnts/servo,pyfisch/servo,KiChjang/servo,thiagopnts/servo,sadmansk/servo,anthgur/servo,larsbergstrom/servo,canaltinova/servo,cbrewster/servo,pyfisch/servo,cbrewster/servo,SimonSapin/servo,emilio/servo,mbrubeck/servo,mattnenterprise/servo,ConnorGBrewster/servo,CJ8664/servo,DominoTree/servo,ConnorGBrewster/servo,avadacatavra/servo,cbrewster/servo,dati91/servo,upsuper/servo,fiji-flo/servo,DominoTree/servo,splav/servo,larsbergstrom/servo,mattnenterprise/servo,rnestler/servo,jimberlage/servo,mattnenterprise/servo,anthgur/servo,canaltinova/servo,dsandeephegde/servo,szeged/servo,sadmansk/servo,pyfisch/servo,upsuper/servo,dsandeephegde/servo,jimberlage/servo,paulrouget/servo,jimberlage/servo,CJ8664/servo,mbrubeck/servo,anthgur/servo,cbrewster/servo,szeged/servo,splav/servo,mbrubeck/servo,fiji-flo/servo,ConnorGBrewster/servo,szeged/servo,rnestler/servo,peterjoel/servo,peterjoel/servo,avadacatavra/servo,dsandeephegde/servo,ConnorGBrewster/servo,pyfisch/servo,peterjoel/servo,CJ8664/servo,eddyb/servo,rnestler/servo,peterjoel/servo,avadacatavra/servo,saneyuki/servo,pyfisch/servo,emilio/servo,DominoTree/servo,nnethercote/servo,canaltinova/servo,KiChjang/servo,szeged/servo,dati91/servo,nnethercote/servo,cbrewster/servo,paulrouget/servo,avadacatavra/servo,CJ8664/servo,emilio/servo,KiChjang/servo,szeged/servo,mattnenterprise/servo,cbrewster/servo,peterjoel/servo,saneyuki/servo,dati91/servo,dsandeephegde/servo,peterjoel/servo,larsbergstrom/servo,peterjoel/servo,SimonSapin/servo,ConnorGBrewster/servo,CJ8664/servo,KiChjang/servo,szeged/servo,anthgur/servo,anthgur/servo,rnestler/servo,dati91/servo,fiji-flo/servo,sadmansk/servo,SimonSapin/servo,jimberlage/servo,dsandeephegde/servo,sadmansk/servo,notriddle/servo,mattnenterprise/servo,fiji-flo/servo,emilio/servo,mbrubeck/servo,saneyuki/servo,splav/servo,pyfisch/servo,pyfisch/servo,canaltinova/servo,mattnenterprise/servo,saneyuki/servo,thiagopnts/servo,rnestler/servo,SimonSapin/servo,cbrewster/servo,KiChjang/servo,sadmansk/servo,notriddle/servo,mbrubeck/servo,SimonSapin/servo,eddyb/servo,eddyb/servo,rnestler/servo,CJ8664/servo,pyfisch/servo,paulrouget/servo,canaltinova/servo,paulrouget/servo,jimberlage/servo,cbrewster/servo,nnethercote/servo,notriddle/servo,CJ8664/servo,saneyuki/servo,notriddle/servo,nnethercote/servo,ConnorGBrewster/servo,emilio/servo,splav/servo,pyfisch/servo,DominoTree/servo,szeged/servo,thiagopnts/servo,jimberlage/servo