Add specs for dotpay confirmation
user
```ruby
require 'rails_helper'

def post_params
  {"id"=>"767542", "operation_number"=>"M9283-8213", "operation_type"=>"payment", "operation_status"=>"completed", "operation_amount"=>"104.36", "operation_currency"=>"PLN", "operation_original_amount"=>"24.60", "operation_original_currency"=>"EUR", "operation_datetime"=>"2017-08-04 17:48:29", "control"=>"280533fa22fb47a95cac", "description"=>"InJobs.pl usługi premium", "email"=>"mis@uszatek.pl", "p_info"=>"Test User (k.j.moroz@gmail.com)", "p_email"=>"k.j.moroz@gmail.com", "channel"=>"246", "signature"=>"a8df51ef3621d4ce8c684d815e1ef7ea77821da6472afdfb5e8c368ac734574f"}
end

RSpec.describe "Dotpay confirmation", type: :request do
  let!(:order) { FactoryGirl.create(:order, unique_token: "280533fa22fb47a95cac") }

  before(:each) do
    post '/api/dotpay/confirm_payment', params: post_params
    order.reload
  end

  it "sets order status and renders OK" do
    expect(order.payment_status).to eq('completed')
  end

  it "sets user's premium_services" do
    expect(order.user.premium_services).to eq(order.to_h)
  end

  it "returns OK" do
    expect(response.body).to eq('OK')
  end

  it "response type is text/plain" do
    expect(response.content_type).to eq('text/plain')
  end
end
```
assistant