use correct format in the test for images

Author: kepano

test/command/8853.md

@@ -1,6 +1,6 @@
 ```
 % pandoc -f markdown+wikilinks_title_after_pipe --wrap=none
-[[hi]] and ![[hi]]
+[[hi]] and ![[hi.jpg]]
 ^D
-<p><a href="hi" class="wikilink">hi</a> and <img src="hi" class="wikilink" alt="hi" /></p>
+<p><a href="hi" class="wikilink">hi</a> and <img src="hi.jpg" class="wikilink" alt="hi" /></p>
 ```