Locally scope `i` in sweepDown and sweepUp
Locally scope `i` in sweepDown and sweepUp

Fixes #127

9n/dagre,abduld/dagre,9n/dagre,cpettitt/dagre,shelsonjava/dagre,witcxc/dagre,tylingsoft/dagre-layout,GerHobbelt/dagre,abduld/dagre,GerHobbelt/dagre,9n/dagre,GerHobbelt/dagre,cpettitt/dagre,kdawes/dagre,rwl/dagre,kdawes/dagre,lmcorbo/dagre,cpettitt/dagre,shelsonjava/dagre,lmcorbo/dagre,kdawes/dagre,witcxc/dagre,shelsonjava/dagre,abduld/dagre,tylingsoft/dagre-layout,lmcorbo/dagre