Update 2014-04-21-write-a-simple-nodejs-mongodb-web-service-for-an-ios-app.md

There is a typo in line 568.  `mongd --dbpath '~/somepath'` should be `mongod --dbpath '~/somepath'`
Merge pull request #2 from nnabuuu/patch-1

Update 2014-04-21-write-a-simple-nodejs-mongodb-web-service-for-an-ios-a...