Update garbage_collection.md
Update garbage_collection.md
lylei/dfs,myawan/bfs-1,myawan/bfs-1,myawan/bfs-1,imotai/bfs,00k/ToyDFS,baidu/bfs,myawan/bfs-1,yvxiang/dfs,yvxiang/coverage_for_bfs,yvxiang/coverage_for_bfs,lylei/dfs,yvxiang/dfs,bluebore/bfs,yvxiang/dfs,bluebore/dfs,bluebore/bfs,linyvxiang/dfs,linyvxiang/dfs,yvxiang/coverage_for_bfs,baidu/bfs,00k/ToyDFS,baidu/bfs,lylei/dfs,bluebore/dfs,bluebore/bfs,baidu/bfs,yvxiang/coverage_for_bfs,linyvxiang/dfs,yvxiang/dfs,imotai/bfs,imotai/bfs,lylei/dfs,bluebore/dfs