error app.js

module.js:457
    throw err;
    ^

Error: Cannot find module 'yargs'
    at Function.Module._resolveFilename (module.js:455:15)
    at Function.Module._load (module.js:403:25)
    at Module.require (module.js:483:17)
    at require (internal/module.js:20:19)
    at Object.<anonymous> (/home/jza/public_html/node-sentinel/src/app.js:49:6)
    at Module._compile (module.js:556:32)
    at Object.Module._extensions..js (module.js:565:10)
    at Module.load (module.js:473:32)
    at tryModuleLoad (module.js:432:12)
    at Function.Module._load (module.js:424:3)