fix some grammar in Clock.html

docs/api/zh/core/Clock.html

@@ -11,7 +11,7 @@
 		<h1>[name]</h1>
 		<p class="desc">
 			该对象用于跟踪时间。如果[link:https://developer.mozilla.org/en-US/docs/Web/API/Performance/now performance.now]可用，则
-			Clock 对象通过该方法实现，否则通过歉精准的[link:https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Date/now Date.now]实现。
+			Clock 对象通过该方法实现，否则回落到使用略欠精准的[link:https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Date/now Date.now]来实现。
 		</p>