remove rrdtool dependency
remove rrdtool dependency

jojohappy/falcon-plus,Cepave/open-falcon-backend,jojohappy/falcon-plus,open-falcon/graph,taomaree/falcon-plus,trigrass2/graph,yubo/graph,Cepave/open-falcon-backend,yubo/graph,masato25/open-falcon-backend,Cepave/open-falcon-backend,taomaree/falcon-plus,jojohappy/falcon-plus,trigrass2/graph,masato25/open-falcon-backend,masato25/open-falcon-backend,taomaree/falcon-plus,open-falcon/falcon-plus,Cepave/open-falcon-backend,masato25/open-falcon-backend,taomaree/falcon-plus,open-falcon/falcon-plus,Cepave/open-falcon-backend,Cepave/open-falcon-backend,jojohappy/falcon-plus,open-falcon/falcon-plus,masato25/open-falcon-backend,jojohappy/falcon-plus,open-falcon/falcon-plus,jojohappy/falcon-plus,taomaree/falcon-plus,masato25/open-falcon-backend,open-falcon/falcon-plus,taomaree/falcon-plus,open-falcon/graph