perf(Menu): change some component to PureComponent

close #77

Author: ZxBing0066

src/components/Menu/Item.jsx

@@ -1,11 +1,11 @@
-import React, { Component } from 'react';
+import React, { PureComponent } from 'react';
 import PropTypes from 'prop-types';
 
-import Checkbox from 'components/Checkbox';
+import Checkbox from 'src/components/Checkbox';
 
 import { ItemWrap } from './style';
 
-class Item extends Component {
+class Item extends PureComponent {
     static propTypes = {
         /** item的唯一键 */
         itemKey: PropTypes.any,

src/components/Select/Option.jsx

@@ -1,10 +1,10 @@
-import React, { Component } from 'react';
+import React, { PureComponent } from 'react';
 import PropTypes from 'prop-types';
 
 import { OptionWrap } from './style';
 import { SelectContext } from './Select';
 
-class Option extends Component {
+class Option extends PureComponent {
     static propTypes = {
         /** 值 */
         value: PropTypes.any,

src/components/Select/Select.jsx

@@ -173,7 +173,7 @@ class Select extends Component {
             }
         }
     };
-    renderPopup = theme => {
+    renderPopup = () => {
         const { search, children, onChange, multiple, showSelectAll, value, options } = this.props;
         const { searchValue, itemTree } = this.state;
         const Options = this.renderOptions(options);