Fixed oauth2 workflow doc. A wrong argument name was being used in Web
Application Flow.

* Fixed doc of oauth2 workflow.
* Web Application Flow defined a variable called `client_secret`.
* We intended to use `client_secret`, but were accidentally calling it
`secret`. Changed `secret` to say `client_secret`.
Merge pull request #114 from akshar-raaj/master

Fixed oauth2 workflow doc. A wrong argument name was being used in Web Application Flow