Error: Cannot find module 'webdriverio'

[flik]

I followed all of your instructions on http://webdriveriotutorial.blogspot.com/
and then tried to run and get error

D:\xampp\htdocs\automation\WebDriverIOTutorial>mocha tutorial1.js
module.js:471
    throw err;
    ^

Error: Cannot find module 'webdriverio'
    at Function.Module._resolveFilename (module.js:469:15)
    at Function.Module._load (module.js:417:25)
    at Module.require (module.js:497:17)
    at require (internal/module.js:20:19)
    at Object.<anonymous> (D:\xampp\htdocs\automation\WebDriverIOTutorial\tutori
al1.js:14:19)
    at Module._compile (module.js:570:32)
    at Object.Module._extensions..js (module.js:579:10)
    at Module.load (module.js:487:32)
    at tryModuleLoad (module.js:446:12)
    at Function.Module._load (module.js:438:3)
    at Module.require (module.js:497:17)
    at require (internal/module.js:20:19)
    at C:\Users\feb2018\AppData\Roaming\npm\node_modules\mocha\lib\mocha.js:231:
27
    at Array.forEach (native)
    at Mocha.loadFiles (C:\Users\feb2018\AppData\Roaming\npm\node_modules\mocha\
lib\mocha.js:228:14)
    at Mocha.run (C:\Users\feb2018\AppData\Roaming\npm\node_modules\mocha\lib\mo
cha.js:536:10)
    at Object.<anonymous> (C:\Users\feb2018\AppData\Roaming\npm\node_modules\moc
ha\bin\_mocha:582:18)
    at Module._compile (module.js:570:32)
    at Object.Module._extensions..js (module.js:579:10)
    at Module.load (module.js:487:32)
    at tryModuleLoad (module.js:446:12)
    at Function.Module._load (module.js:438:3)
    at Module.runMain (module.js:604:10)
    at run (bootstrap_node.js:394:7)
    at startup (bootstrap_node.js:149:9)
    at bootstrap_node.js:509:3