TypeError: discover is not a function

[MuhendisBey]

if you run " git clone https://github.com/corenova/yang-express;" then run "cd yang-express" then run "npm install"

and finally you run "yang-express example/example-petstore.yang" or "npm run example:petstore"

you get this error message:

yang-express@2.1.8 example:petstore /home/bay/workspace/tmp/yang-express
NODE_ENV=example NODE_APP_INSTANCE=petstore bin/yang-express --router restjson example-petstore

TypeError: discover is not a function
at Method.rpc(listen) (/home/bay/workspace/tmp/yang-express/yang-web-store.js:36:13)
at Method.do (/home/bay/workspace/tmp/yang-express/node_modules/yang-js/lib/method.js:42:64)
at Object. (/home/bay/workspace/tmp/yang-express/bin/yang-express:45:27)
at Module._compile (internal/modules/cjs/loader.js:1076:30)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:1097:10)
at Module.load (internal/modules/cjs/loader.js:941:32)
at Function.Module._load (internal/modules/cjs/loader.js:782:14)
at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:72:12)
at internal/main/run_main_module.js:17:47