Update images.md

first pass at sorting textpattern/textpattern#1764

Author: petecooper

tags/images.md

@@ -103,7 +103,7 @@ Tag will accept the following attributes (**case-sensitive**) as well as the {%
 `caption`. \\
 `category`. \\
 `date`. \\
-`extension` (image extension). \\
+`ext` (image extension). \\
 `h` (image `height` attribute). \\
 `id` (image id#). \\
 `name` (image name). \\