修复其他主题不能预览问题

examples/components/App.tsx

@@ -385,6 +385,7 @@ export class App extends React.PureComponent {
           </div>
 
           {React.cloneElement(this.props.children, {
+            key: theme.value,
             ...this.props.children.props,
             setNavigations: this.setNavigations,
             setAsideFolded: this.setAsideFolded,

examples/components/MdRenderer.tsx

@@ -46,6 +46,7 @@ class CodePreview extends React.Component {
             show
           >
             <PopOver
+              theme={(rest as any).theme}
               offset={{x: 0, y: -height}}
               style={{height}}
               className=":MDPreview-shcema-preview-popover"

examples/components/Play.jsx

@@ -85,6 +85,7 @@ export default class PlayGround extends React.Component {
       }
     };
     this.env = {
+      session: 'doc',
       updateLocation: () => {},
       fetcher: config => {
         config = {
@@ -182,7 +183,9 @@ export default class PlayGround extends React.Component {
     const props = {
       ...this.schemaProps,
       theme: this.props.theme,
-      locale: this.props.locale
+      locale: this.props.locale,
+      affixHeader: false,
+      affixFooter: false
     };
 
     if (!this.props.useIFrame) {