Fix multiple @extends in stream.js
Fix multiple @extends in stream.js

It's not possible to @extends two different classes (see
http://code.google.com/p/closure-compiler/issues/detail?id=250).  This
was causing the following error:

stream.js:209: WARNING - Bad type annotation. type annotation incompatible with other annotations
 * @extends stream.Writable
                           ^

From source inspection, Duplex extends Readable and implements Writable.
Update the annotations to reflect this.

Signed-off-by: Kevin Locke <ffb4761cba839470133bee36aeb139f58d7dbaa9@kevinlocke.name>

dcodeIO/node.js-closure-compiler-externs,keunwoo/node.js-closure-compiler-externs