POST to request-promise-native has no formdata

This is probably something stupid I'm overlooking, but I am trying to use request-promise-native to POST to a form, and the response I get looks like the form data I sent is blank.

Example: This works with the standard request:

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);
 });

Correctly produces:

<html>
<title>Local Apparent Sideral Time </title>
<body>
<center>
<HR><h1>Local Apparent Sidereal Time</h1><HR>
<TABLE BORDER=4 ALIGN=CENTER VALIGN=CENTER CELLPADDING=5>
<TR><TH> SANTA CRUZ              , CA</TH>
<TR><TH> Longitude -122.04 degrees </TH>
<TR><TD ALIGN=CENTER><H1> 02:56 LST </H1></TD>
</TABLE>
</center>
</body>
</html>

But this 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);
    });

produces this result as if it didn't get the formData:

<html>
<title>Local Apparent Sideral Time </title>
<body>
<center>
<HR><h1>Local Apparent Sidereal Time</h1><HR>
<HR><h1>Coordinates for                         , FO not found</h1><HR>
</center>
</body>
</html>

Am I forgetting brackets or punctuation or something? This seems to me to be identical to the example in the request-promise documentation.