How to compile latest version of zerotier?

i already compiled latest openwrt for my zyxel p-2812. but zerotier package is 1.6.6. but latest version is 1.8.4. i tried to compile accroding to directives on zerotier-openwrt github pages. but every time builded 1.6.6 not 1.8.4.

so how can i build latest zerotier and embed my firmware???