[FIX] Custom OAuth Bug

[PrajvalRaval]

This pull request fixes a bug in Custom OAuth flow of Rocket.Chat. Custom OAuth right now depends upon the services block of user data to validate and find user from the database. Following is a sample services block, with alexapnr as OAuth servicename:

services: {
  password: {
    bcrypt: '$2b$10$dWQ7Vjfb8jRaT15/wpqdZOZXLmHOM.rx69GQjos.cUM4Oqyszr.ry',
    reset: [ Object ]
  },
  email: {
    verificationTokens: [ Array ]
  },
  resume: {
    loginTokens: [ Array ]
  },
  alexapnr: {
    id: 'Dv8cbqqFYuG6cvmWP',
    accessToken: '57fbbe8c1a16d4b2181e12fc52cfd6e634eaede5',
    email: 'ravalprajval@gmail.com',
    expiresAt: 1583579264954,
    name: 'Prajval Raval',
    roles: [ Array ],
    username: 'prajval.raval'
  }
}

In the above block you can see, the data is stored as services.[serviceName].id: userId but in current Rocket Chat code, we are sending the query as:

const query = { username, [`services.${ serviceName }.id`]: serviceName };

instead of,

const query = { username, [`services.${ serviceName }.id`]: userId };

[PrajvalRaval]

@MarcosSpessatto Please review it. Thanks.