Fix nit of chrome.commands doc: invalid json format.

chrome/common/extensions/docs/templates/intros/commands.html

 <h2 id="manifest">Manifest</h2>
 <p>
 You must set manifest_version to (at least) 2 to use this API.
 </p>
 
 <h2 id="usage">Usage</h2>
 <p>The commands API allows you to define specific commands, and bind them to a
 default key combination. Each command your extension accepts must be listed in
 the manifest as an attribute of the 'commands' manifest key. An extension can
 have many commands but only 4 suggested keys can be specified. The user can
@@ skipping 26 matching lines @@
     "_execute_browser_action": {
       "suggested_key": {
         "windows": "Ctrl+Shift+Y",
         "mac": "Command+Shift+Y",
         "chromeos": "Ctrl+Shift+U",
         "linux": "Ctrl+Shift+J"
       }
     },
     "_execute_page_action": {
       "suggested_key": {
-        "default": "Ctrl+E"
+        "default": "Ctrl+E",
         "windows": "Alt+P",
-        "mac": "Option+P",
+        "mac": "Option+P"
       }
     }
   }</b>,
   ...
 }</pre>
 
 <p>In your background page, you can bind a handler to each of the commands
 defined in the manifest (except for '_execute_browser_action' and
 '_execute_page_action') via onCommand.addListener. For example:</p>
 
 <pre>
 chrome.commands.onCommand.addListener(function(command) {
   console.log('Command:', command);
 });
 </pre>
 
 <p>The '_execute_browser_action' and '_execute_page_action' commands are
 reserved for the action of opening your extension's popups. They won't normally
 generate events that you can handle. If you need to take action based on your
 popup opening, consider listening for an 'onDomReady' event inside your popup's
 code.
 </p>