docs: fix immutable demo embedding (#189)

packages/dx-react-grid/docs/guides/immutability.md

@@ -7,16 +7,23 @@ DevExpress Data Grid for React conforms to the React [optimization principles](h
 You can use the [seamless-immutable](https://github.com/rtfeldman/seamless-immutable) library to make a React Grid state immutable.
 The following example demonstrates how to initialize an immutable state:
 
-    this.state = {
-      data: Immutable({
-        // the state fields
-      })
-    };
+```js
+this.state = {
+  data: Immutable({
+    // the state fields
+  })
+};
+```
 
 Then you can use the state in a usual way because `seamless-immutable` keeps backwards-compatibility with normal Arrays and Objects.
 
 The following demo demonstrates the React Grid with `seamless-immutable` in action:
 
-[DEMO](http://devexpress.github.io/devextreme-reactive/react/grid/demos/#/immutability/seamless-immutable)
+Bootstrap 3:
+[Demo](http://devexpress.github.io/devextreme-reactive/react/grid/demos/#/bootstrap3/immutability/seamless-immutable) |
+[Source](https://github.com/DevExpress/devextreme-reactive/tree/master/packages/dx-react-demos/src/bootstrap3/immutability/seamless-immutable.jsx)
+
+Material UI:
+[Demo](http://devexpress.github.io/devextreme-reactive/react/grid/demos/#/material-ui/immutability/seamless-immutable) |
+[Source](https://github.com/DevExpress/devextreme-reactive/tree/master/packages/dx-react-demos/src/material-ui/immutability/seamless-immutable.jsx)
 
-[SOURCE](https://github.com/DevExpress/devextreme-reactive/tree/master/packages/dx-react-demos/src/bootstrap3/immutability/seamless-immutable.jsx)