Allow ubuntu_install_darknet.sh to work in both 18.04 and 16.04 (#5574)
Allow ubuntu_install_darknet.sh to work in both 18.04 and 16.04 (#5574)


dmlc/tvm,Laurawly/tvm-1,Laurawly/tvm-1,sxjscience/tvm,tqchen/tvm,tqchen/tvm,dmlc/tvm,dmlc/tvm,dmlc/tvm,tqchen/tvm,tqchen/tvm,tqchen/tvm,Laurawly/tvm-1,Laurawly/tvm-1,Laurawly/tvm-1,sxjscience/tvm,sxjscience/tvm,Laurawly/tvm-1,dmlc/tvm,Laurawly/tvm-1,tqchen/tvm,sxjscience/tvm,sxjscience/tvm,Laurawly/tvm-1,sxjscience/tvm,sxjscience/tvm,dmlc/tvm,tqchen/tvm,Laurawly/tvm-1,dmlc/tvm,sxjscience/tvm,tqchen/tvm,Laurawly/tvm-1,sxjscience/tvm,tqchen/tvm,dmlc/tvm,dmlc/tvm,tqchen/tvm