Compatibility with social_api/social_auth 3.*

Problem/Motivation

As the active branches of social_api and social_auth are 3.x now, this module should.

Steps to reproduce

ddev composer require drupal/social_auth_discord:2.x-dev

./composer.json has been updated
Running composer update drupal/social_auth_discord
Loading composer repositories with package information
Updating dependencies
Lock file operations: 5 installs, 0 updates, 0 removals
  - Locking drupal/social_api (2.0.0-rc4)
  - Locking drupal/social_auth (2.0.0-rc4)
  - Locking drupal/social_auth_discord (dev-2.x 34a7466)
  - Locking league/oauth2-client (2.6.0)
  - Locking wohali/oauth2-discord-new (1.1.0)
Writing lock file
Installing dependencies from lock file (including require-dev)
Package operations: 5 installs, 0 updates, 0 removals
  - Downloading drupal/social_api (2.0.0-rc4)
  - Downloading wohali/oauth2-discord-new (1.1.0)
  - Downloading drupal/social_auth (2.0.0-rc4)
  - Syncing drupal/social_auth_discord (dev-2.x 34a7466) into cache
  - Installing league/oauth2-client (2.6.0): Extracting archive
  - Installing drupal/social_api (2.0.0-rc4): Extracting archive
  - Installing wohali/oauth2-discord-new (1.1.0): Extracting archive
  - Installing drupal/social_auth (2.0.0-rc4): Extracting archive
  - Installing drupal/social_auth_discord (dev-2.x 34a7466): Cloning 34a7466956 from cache

Proposed resolution

* Update dependencies to support social_api 3.* and social_auth 3.*

Remaining tasks

* patch

User interface changes

-

API changes

-

Data model changes

-