Update typescript definitions to match the latest SDK v3.0.2

[shlok-kothari]

#100

[shlok-kothari]

oauth-jsclient/src/OAuthClient.js

Line 88 in 43a597b

OAuthClient.migrate_production = 'https://developer.api.intuit.com/v2/oauth2/tokens/migrate';

I wasn't sure if constants such as these also had to be included in this file? Lines 79-109 from OAuthClient.js..I did see some constants like the scopes and environment already defined so wanted to clarify

[shlok-kothari]

I'm unable to run the sample app, for some reason `req.query.json.clientId` is not being treated as a property of a JSON object, though I did verify that `typeof(req.query.json)` is object. I tried `JSON.parse(req.query.json.toString()).clientId` but that gives me a different error: `SyntaxError: Unexpected token o in JSON at position 1`

@abisalehalliprasan I had a couple of questions, this is my first time working with typescript so I'm sorry if it was something obvious!

[abisalehalliprasan]

Thanks @shlok-kothari. I will take a look at the PR 👍