Fix incorrect parameter in audio_track_set_key_stream.

The description for audio_track_set_key_stream referenced a parameter called offset, which is not a parameter for that method. The description now references the correct parameter, stream.

doc/classes/Animation.xml

@@ -168,7 +168,7 @@
 			<argument index="2" name="stream" type="Resource">
 			</argument>
 			<description>
-				Sets the stream of the key identified by [code]key_idx[/code] to value [code]offset[/code]. The [code]track_idx[/code] must be the index of an Audio Track.
+				Sets the stream of the key identified by [code]key_idx[/code] to value [code]stream[/code]. The [code]track_idx[/code] must be the index of an Audio Track.
 			</description>
 		</method>
 		<method name="bezier_track_get_key_in_handle" qualifiers="const">