doc: fix type in stream doc

Extend return type of `read()` method with `any` which is a
valid return type for readable streams in object mode.

Author: KonanMentor

doc/api/stream.md

@@ -954,7 +954,7 @@ added: v0.9.4
 -->
 
 * `size` {number} Optional argument to specify how much data to read.
-* Returns: {string|Buffer|null}
+* Returns: {string|Buffer|null|any}
 
 The `readable.read()` method pulls some data out of the internal buffer and
 returns it. If no data available to be read, `null` is returned. By default,