use the upload field to send the file, accepting a ReadStream

A `ReadStream` is necessary here because of how SuperAgent's internals are implemented: `.attach` requires an explicit filename (which I don't want to do), and `.field` can infer the filename, but only from `ReadStream`s or other request objects.

README.md

@@ -28,8 +28,8 @@ deploy({
   // the version to publish
   version: '1.0.0',
 
-  // a Buffer or string containing a .zip (WebExtensions) or .xpi (Add-on SDK)
-  src: fs.readFileSync('path/to/zipped/extension.zip'),
+  // a ReadStream containing a .zip (WebExtensions) or .xpi (Add-on SDK)
+  src: fs.createReadStream('path/to/zipped/extension.zip'),
 }).then(function() {
   // success!
 }, function(err) {

index.js

@@ -42,8 +42,7 @@ module.exports = function deploy(options) {
 		request
 			.put('https://addons.mozilla.org/api/v3/addons/' + extensionId + '/versions/' + extensionVersion + '/')
 			.set('Authorization', 'JWT ' + token)
-			.type('multipart/form-data')
-			.send(srcFile)
+			.field('upload', srcFile)
 			.end(function(err, response) {
 				if (err) {
 					var msg;

test/test.js

@@ -109,8 +109,6 @@ test.serial('full deploy', async t => {
 	t.is(publishReq.match[1], 'someId');
 	t.is(publishReq.match[2], 'someVersion');
 	t.regex(publishReq.headers['Authorization'], /^JWT /);
-	t.is(publishReq.headers['Content-Type'], 'multipart/form-data');
-	t.is(publishReq.params, 'someSrc');
 
 	// throws if invalid
 	jwt.verify(publishReq.headers['Authorization'].slice(4), 'someSecret', {