docs: Rewrite TreeSelect demos to ES6 component

components/tree-select/demo/basic.md

@@ -17,16 +17,14 @@ The most basic usage.
 import { TreeSelect } from 'antd';
 const TreeNode = TreeSelect.TreeNode;
 
-const Demo = React.createClass({
-  getInitialState() {
-    return {
+class Demo extends React.Component {
+  state = {
     value: undefined,
-    };
-  },
-  onChange(value) {
+  }
+  onChange = (value) => {
     console.log(arguments);
     this.setState({ value });
-  },
+  }
   render() {
     return (
       <TreeSelect
@@ -50,8 +48,8 @@ const Demo = React.createClass({
         </TreeNode>
       </TreeSelect>
     );
-  },
-});
+  }
+}
 
 ReactDOM.render(<Demo />, mountNode);
 ````

components/tree-select/demo/checkable.md

@@ -45,16 +45,14 @@ const treeData = [{
   }],
 }];
 
-const Demo = React.createClass({
-  getInitialState() {
-    return {
+class Demo extends React.Component {
+  state = {
     value: ['0-0-0'],
-    };
-  },
-  onChange(value) {
+  }
+  onChange = (value) => {
     console.log('onChange ', value, arguments);
     this.setState({ value });
-  },
+  }
   render() {
     const tProps = {
       treeData,
@@ -69,8 +67,8 @@ const Demo = React.createClass({
       },
     };
     return <TreeSelect {...tProps} />;
-  },
-});
+  }
+}
 
 ReactDOM.render(<Demo />, mountNode);
 ````

components/tree-select/demo/treeData.md

@@ -36,16 +36,14 @@ const treeData = [{
   key: '0-1',
 }];
 
-const Demo = React.createClass({
-  getInitialState() {
-    return {
+class Demo extends React.Component {
+  state = {
     value: undefined,
-    };
-  },
-  onChange(value) {
+  }
+  onChange = (value) => {
     console.log(arguments);
     this.setState({ value });
-  },
+  }
   render() {
     return (
       <TreeSelect
@@ -58,8 +56,8 @@ const Demo = React.createClass({
         onChange={this.onChange}
       />
     );
-  },
-});
+  }
+}
 
 ReactDOM.render(<Demo />, mountNode);
 ````