Why not use sed?
sed -i '$ a src-git node https://github.com/nxhack/openwrt-node-packages.git' feeds.conf
The run
./scripts/feeds update -a
./scripts/feeds install -a
if your after the .config file i normaly use
wget https://dc502wrt.org/snapshots/r10307/targets/mvebu/cortexa9/config.seed -O .config
make defconfig
then I use
make menuconfig
After