mutualUsers = async (session, user) => {
  let myFollowings = await db.query(
      'SELECT follow_system.follow_id, follow_system.follow_to AS user, follow_system.follow_to_username AS username, users.firstname, users.surname FROM follow_system, users WHERE follow_system.follow_by=? AND follow_system.follow_to = users.id',
      [session]
    ),
    userFollowers = await db.query(
      'SELECT follow_system.follow_id, follow_system.follow_by AS user, follow_system.follow_by_username AS username, users.firstname, users.surname FROM follow_system, users WHERE follow_system.follow_to=? AND follow_system.follow_by = users.id',
      [user]
    ),
    mutuals = intersectionBy(myFollowings, userFollowers, 'user')

  return mutuals
}
Returns mutual users
Returns mutual users of session & user
@param {Number} session Session ID
@param {Number} user User ID