Change zip link to txt on Export page

"zip" doesn't really describe what the posts themselves are exported as.
"txt" does.

templates/user/export.tmpl

@@ -13,7 +13,7 @@
 		<tr>
 			<th>Posts</th>
 			<td><p class="text-cta"><a href="/me/posts/export.csv">CSV</a></p></td>
-			<td><p class="text-cta"><a href="/me/posts/export.zip">ZIP</a></p></td>
+			<td><p class="text-cta"><a href="/me/posts/export.zip">TXT</a></p></td>
 		</tr>
 		<tr>
 			<th>User + Blogs + Posts</th>