check for pipe method only (part 2)

Don't know why I didn't replace all calls to isStream. This fix
error on passing Stream from multiparty.

Related 5205e7260f

index.js

@@ -160,7 +160,7 @@ function asStream(opts) {
 	ee.on('request', function (req) {
 		proxy.emit('request', req);
 
-		if (isStream.readable(opts.body)) {
+		if (isStream(opts.body)) {
 			opts.body.pipe(req);
 			return;
 		}
@@ -240,7 +240,7 @@ function normalizeArguments(url, opts) {
 	var body = opts.body;
 
 	if (body) {
-		if (typeof body !== 'string' && !Buffer.isBuffer(body) && !isStream.readable(body) && !isPlainObj(body)) {
+		if (typeof body !== 'string' && !Buffer.isBuffer(body) && !isStream(body) && !isPlainObj(body)) {
 			throw new Error('options.body must be a ReadableStream, string, Buffer or plain Object');
 		}
 
@@ -251,7 +251,7 @@ function normalizeArguments(url, opts) {
 			body = opts.body = querystring.stringify(body);
 		}
 
-		if (opts.headers['content-length'] === undefined && opts.headers['transfer-encoding'] === undefined && !isStream.readable(body)) {
+		if (opts.headers['content-length'] === undefined && opts.headers['transfer-encoding'] === undefined && !isStream(body)) {
 			var length = typeof body === 'string' ? Buffer.byteLength(body) : body.length;
 			opts.headers['content-length'] = length;
 		}