Update documented return type of toStream (#62)

Document that `toStream` can also return an `ArrayStream`,
if one is passed.

Author: twiss

lib/streams.js

@@ -4,12 +4,11 @@ import { ArrayStream, Writer } from './writer.js';
 
 /**
  * Convert data to Stream
- * @param {ReadableStream|Uint8array|String} input  data to convert
- * @returns {ReadableStream} Converted data
+ * @param {ReadableStream|ArrayStream|Uint8array|String} input  data to convert
+ * @returns {ReadableStream|ArrayStream} Converted data
  */
 function toStream(input) {
-  let streamType = isStream(input);
-  if (streamType) {
+  if (isStream(input)) {
     return input;
   }
   return new ReadableStream({