doc: fix a trivial mistake, expected -> unexpected

In this context, 'expected' looks strange word.

doc/api/stream.md

@@ -1503,9 +1503,9 @@ Implementers, and only from within the `readable._read()` method.
 It is recommended that errors occurring during the processing of the
 `readable._read()` method are emitted using the `'error'` event rather than
 being thrown. Throwing an Error from within `readable._read()` can result in
-expected and inconsistent behavior depending on whether the stream is operating
-in flowing or paused mode. Using the `'error'` event ensures consistent and
-predictable handling of errors.
+unexpected and inconsistent behavior depending on whether the stream is
+operating in flowing or paused mode. Using the `'error'` event ensures
+consistent and predictable handling of errors.
 
 ```js
 const Readable = require('stream').Readable;