title: fetch patch request is not allowed
body: <p>I have two apps one is a react front end and the second one is the rails-api app.</p>
  
  <p>I have been happily using <a href="https://github.com/matthew-andrews/isomorphic-fetch" rel="noreferrer">isomorphic-fetch</a> till I needed to send PATCH method to the server.</p>
  
  <p>I am getting:</p>
  
  <pre><code>Fetch API cannot load http://localhost:3000/api/v1/tasks. Method patch is not allowed by Access-Control-Allow-Methods in preflight response.
  </code></pre>
  
  <p>but the OPTIONS response from the server includes a PATCH method in a list of Access-Control-Allow-Methods:</p>
  
  <p><a href="https://i.stack.imgur.com/OaF30.png" rel="noreferrer"><img src="https://i.stack.imgur.com/OaF30.png" alt="enter image description here"></a></p>
  
  <p>This is how the fetch is implemented:</p>
  
  <pre><code>const API_URL = 'http://localhost:3000/'                                            
  const API_PATH = 'api/v1/'
  
  fetch(API_URL + API_PATH + 'tasks', {
    headers: {
      'Accept': 'application/json',
      'Content-Type': 'application/json'
    },
    method: 'patch',                                                              
    body: JSON.stringify( { task: task } )                                        
  })
  </code></pre>
  
  <p>POST, GET, DELETE are set up pretty much the same and they are working fine.</p>
  
  <p>Any idea what is going on here?</p>
  
  <p><strong>UPDATE:</strong></p>
  
  <p>Method patch is case sensitive:</p>
  
  <p><a href="https://github.com/github/fetch/blob/master/fetch.js#L200" rel="noreferrer">https://github.com/github/fetch/blob/master/fetch.js#L200</a></p>
  
  <p>Not to sure if this is intended or a bug.</p>
  
  <p><strong>UPDATE 2</strong></p>
  
  <p>This is intended and the method type PATCH needs to be case sensitive.
  Updating the line from fetch method to:</p>
  
  <pre><code>method: 'PATCH'
  </code></pre>
  
  <p>fixes the problem.</p>
  
  <p><a href="https://github.com/github/fetch/issues/254" rel="noreferrer">https://github.com/github/fetch/issues/254</a></p>