Update figure description in Overview document (#2676)

It used the wrong reference to the image...

epub33/overview/index.html

@@ -108,7 +108,7 @@ <h3>Reading this document</h3>
 				<details id="fig-epub-structure-diagram" class="desc">
 					<summary style="font-weight: normal; font-style: italic">Image description</summary>
 					<p>'EPUB (OCF) container' as the outer most component which encapsulates the 'EPUB publication'
-						containing two documents 'Publication Document' and 'EPUB navigation document' along with a
+						containing two documents 'Package Document' and 'EPUB navigation document' along with a
 						inner component labelled 'publication resources' which contains multiple 'EPUB content
 						documents' (XHTML, SVG), and multiple 'Other resources' (CSS, png, mp3, mov, etc.). </p>
 				</details>