Fix small mistake in docs for chrome.tts

Change-Id: Ife1502a2d92a9f9ce9743e6fae95419bfd956a1e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2384451
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Auto-Submit: John Palmer <jopalmer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809038}

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

@@ -76,7 +76,7 @@ pass an event listener in the options to <code>speak()</code>, like this:</p>
     utterance,
     {
       onEvent: function(event) {
-        console.log('Event ' + event.type ' at position ' + event.charIndex);
+        console.log('Event ' + event.type + ' at position ' + event.charIndex);
         if (event.type == 'error') {
           console.log('Error: ' + event.errorMessage);
         }