Version 6.14.1

### 6.14.1
  - Changes
    - Auth: Added a new method: Firebase.Auth.Credential.IsValid().
    - Auth: Added Firebase.Auth.FirebaseAccountLinkException which may be thrown
      by LinkAndRetrieveDataWithCredentialAsync. The exception includes a
      Firebase.Auth.UserInfo object which may contain additional information
      about the user's account.
    - Auth (iOS): Added Firebase.Auth.UserInfo.UpdatedCredential. This
      credential may be valid in FirebaseAccountLinkExceptions indicating that
      the credential may be used to sign into Firebase as the Apple-linked user.