docs(tabs): Update docs and changelog for breaking change to tab chan…

…ge event (#402)

CHANGELOG.md

@@ -59,6 +59,7 @@ Example:
   <mdc-icon>navigate_before</mdc-icon>
 </mdc-tab-bar-scroll-back>
 ```
+* **tabs:** Changed format of change event data from `{activeTabIndex: number}` to `{index: number, tab: MdcTab}`.
 * **select:** Removed `label` setter and `setLabel()` function. Use `placeholder` and `setPlaceholder` instead.
 
 

src/demo-app/components/tab-demo/tab-demo.html

@@ -81,7 +81,7 @@ <h1 mdc-typography-display1>Tabs</h1>
       </thead>
       <tbody>
         <tr>
-          <td><pre>change(activeTabIndex: number)</pre></td>
+          <td><pre>change({index: number, tab: MdcTab})</pre></td>
           <td>Broadcast when a user actions on a tab, resulting in a change in the selected tab.</td>
         </tr>
       </tbody>
@@ -354,7 +354,7 @@ <h1 mdc-typography-display1>Tabs</h1>
 </mdc-toolbar>
 
 <pre mdc-typography-caption>
-Tab Change event: 
+Tab Change event:
   index: {{eventTabIndex}}
 </pre>