feeds.conf: use specific branch of OpenWrt release in node feed

Maintainer of node feed is taking care of separate branches for OpenWrt,
let's use specific version to be sync in other feeds as well instead of
using master branch.

feeds.conf

@@ -3,7 +3,7 @@
 # openwrt https://git.openwrt.org/openwrt/openwrt.git;openwrt-19.07
 
 src-git turrispackages https://gitlab.labs.nic.cz/turris/turris-os-packages.git;master
-src-git node https://github.com/nxhack/openwrt-node-packages.git;master
+src-git node https://github.com/nxhack/openwrt-node-packages.git;openwrt-19.07
 src-git packages https://git.openwrt.org/feed/packages.git;openwrt-19.07
 src-git luci https://git.openwrt.org/project/luci.git;openwrt-19.07
 src-git routing https://git.openwrt.org/feed/routing.git;openwrt-19.07