title: allHeaderFields is not case insensitive when looking up keys
body: <p>I'm using Alamofire to make my API calls.</p>
  <p>Depending on the server I'm using the response headers could be capitalized.</p>
  <p>But as the documentation says for allHeaderFields :</p>
  <blockquote>
  <p>var allHeaderFields: [AnyHashable : Any] { get }</p>
  <p>A dictionary containing all the HTTP header fields received as part of the server’s response. By examining this dictionary clients can see the “raw” header information returned by the HTTP server.</p>
  <p>The keys in this dictionary are the header field names, as received from the server. See RFC 2616 for a list of commonly used HTTP header fields.</p>
  <p>HTTP headers are case insensitive. To simplify your code, certain header field names are canonicalized into their standard form. For example, if the server sends a content-length header, it is automatically adjusted to be Content-Length.</p>
  <p>The returned dictionary of headers is configured to be case-preserving during the set operation (unless the key already exists with a different case), and case-insensitive when looking up keys.</p>
  <p>For example, if you set the header X-foo, and then later set the header X-Foo, the dictionary’s key will be X-foo, but the value will taken from the X-Foo header.</p>
  </blockquote>
  <p>But in my code if I'm doing this :</p>
  <pre><code>if let headers = response.response?.allHeaderFields {
     print(&quot;Access-Token: \(response.response?.allHeaderFields[&quot;Access-Token&quot;])&quot;)
     print(&quot;access-token: \(response.response?.allHeaderFields[&quot;access-token&quot;])&quot;)
     print(&quot;access-token: \(response.response?.allHeaderFields[&quot;Access-token&quot;])&quot;)
  }
  </code></pre>
  <p>In the console I have</p>
  <pre><code>Access-Token: nil
  access-token: Optional(jdRtDzKHNs_i-jt3Lh3a3A)
  access-token: nil
  </code></pre>
  <p>Am I missing something ?</p>