title: Laravel Cashier: newSubscription doesn't create Stripe user
body: <p>It's not clear from the documentation but, from what I've gleaned anecdotally from others' comments and examples, the newSubscription function is supposed to:</p>
  
  <p>a. take the token as created in createToken()</p>
  
  <p>b. create customer in Stripe</p>
  
  <p>c. associate a new subscription with that new customer</p>
  
  <p>d. update Laravel databases accordingly</p>
  
  <p>Is this correct? In my testing, I always get the same message:</p>
  
  <pre><code>"message": "No such customer: tok_********************",
  "exception": "Stripe\Error\InvalidRequest",
  </code></pre>
  
  <p>because Cashier has not in fact created a Stripe user using my token.</p>
  
  <p>Apologies if I'm missing something obvious. Are we supposed to use the Stripe PHP to create Customer and THEN use Cashier to associate a subscription to that customer?</p>