Please look at https://openwrt.org/downloads for the newest packages.
Another release. But without packages for LEDE, since the minimum compiler version has been raised.
Look here for ZeroTier packages of more recent LEDE/OpenWrt releases: https://downloads.openwrt.org/releases/17.01.4/packages/
Please update your libstdcpp package in case you get "symbol not found" errors from zerotier-one/zerotier-cli. See #33 for details.