微调了input-number在chrome下的效果

components/input-number/demo/disabled.md

@@ -12,7 +12,7 @@ var InputNumber = antd.InputNumber;
 var Test = React.createClass({
   getInitialState() {
     return {
-      disabled:false
+      disabled: false
     };
   },
   toggle() {

style/components/inputNumber.less

@@ -93,6 +93,7 @@
         content: "\e600";
         .ie-rotate(2);
         transform: rotate(180deg);
+        -webkit-transform-origin: 47.5% 51%; /* fix chrome position */
       }
     }
   }