title: POST to request-promise-native has no formdata
body: <p>This is probably something stupid I'm overlooking, but I am trying to use <code>request-promise-native</code> to POST to a form, and the response I get looks like the form data I sent is blank.  </p>
  
  <p><strong>Example</strong>:
  This works with the standard <code>request</code>:</p>
  
  <pre><code>const request = require('request');
  request.post({
      url:'http://tycho.usno.navy.mil/cgi-bin/sidereal2-post.sh',
      form: {
          city: 'Santa Cruz',
          state: 'CA'
  }
  },
      function(err,httpResponse,body){
          if (err) {
           return console.log("Error: " + err);
          }
       console.log("got: " + body);
   });
  </code></pre>
  
  <p>Correctly produces:</p>
  
  <pre><code>&lt;html&gt;
  &lt;title&gt;Local Apparent Sideral Time &lt;/title&gt;
  &lt;body&gt;
  &lt;center&gt;
  &lt;HR&gt;&lt;h1&gt;Local Apparent Sidereal Time&lt;/h1&gt;&lt;HR&gt;
  &lt;TABLE BORDER=4 ALIGN=CENTER VALIGN=CENTER CELLPADDING=5&gt;
  &lt;TR&gt;&lt;TH&gt; SANTA CRUZ              , CA&lt;/TH&gt;
  &lt;TR&gt;&lt;TH&gt; Longitude -122.04 degrees &lt;/TH&gt;
  &lt;TR&gt;&lt;TD ALIGN=CENTER&gt;&lt;H1&gt; 02:56 LST &lt;/H1&gt;&lt;/TD&gt;
  &lt;/TABLE&gt;
  &lt;/center&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>But this code</p>
  
  <pre><code>const rp = require('request-promise-native');
  
  const options = {
      method: 'POST',
      uri: 'http://tycho.usno.navy.mil/cgi-bin/sidereal2-post.sh',
      formData: {
          city: 'Santa Cruz',
          state: 'CA'
      },
  };
  
  rp(options)
      .then(function (body) {
          // POST succeeded
          console.log("got: "
          + body);
      })
      .catch(function (err) {
          // POST failed...
          console.log("ERROR: " + err);
      });
  </code></pre>
  
  <p>produces this result as if it didn't get the formData:</p>
  
  <pre><code>&lt;html&gt;
  &lt;title&gt;Local Apparent Sideral Time &lt;/title&gt;
  &lt;body&gt;
  &lt;center&gt;
  &lt;HR&gt;&lt;h1&gt;Local Apparent Sidereal Time&lt;/h1&gt;&lt;HR&gt;
  &lt;HR&gt;&lt;h1&gt;Coordinates for                         , FO not found&lt;/h1&gt;&lt;HR&gt;
  &lt;/center&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>Am I forgetting brackets or punctuation or something?  This seems to me to be identical to the example in the <a href="https://www.npmjs.com/package/request-promise#post-like-html-forms-do" rel="nofollow noreferrer">request-promise documentation</a>.</p>