[css-color-4] update video references for tobie/specref#494

Author: svgeesus

css-color-4/Overview.bs

@@ -174,7 +174,7 @@ Notes On Using Colors</h3>
 
 	Note that this rule does not apply to videos, since untagged video should be presumed to be in ITU.
 	* At below 720p, it is Recommendation ITU-R BT.601 [[!ITU-R-BT.601]]
-	* At 720p, it is SMPTE ST 296 (same colorimetry as 709) [[!SMPTE-ST-296]]
+	* At 720p, it is SMPTE ST 296 (same colorimetry as 709) [[!SMPTE296]]
 	* At 1080p, it is Recommendation ITU-R BT.709 [[!ITU-R-BT.709]]
 
 	Issue(287):