Update video.md (#221)

Update video doc
diff --git a/source/references/components/video.md b/source/references/components/video.md
index 24c363d..36b3af3 100644
--- a/source/references/components/video.md
+++ b/source/references/components/video.md
@@ -19,6 +19,8 @@
 * src: <string> The URL of the video to embed.
 * play-status: <boolean> play | pause. Use it to control video's play/pause status. Default value is pause.
 * auto-play: <boolean> true | false. Use it to control whether it is playing when the page initialization finished. Defalut value is false.
+* poster: &lt;string&gt; <span class="weex-version">v0.18+ & iOS only</span> Post image URL of this video if any.
+* controls: &lt;string&gt; <span class="weex-version">v0.19+</span> If set to 'nocontrols', native video component will hide its play-back control panel.
 
 ## Styles
 common styles: check out [common styles for components](/wiki/common-styles.html)