fix tag

doc/todo/tmplvars_plugin.mdwn

@@ -1,6 +1,6 @@
 A simple plugin to allow per-page customization of a template by passing paramaters to HTML::Template. For those times when a whole pagetemplate is too much work. --Ethan
 
-[[!tags patch]]
+[[!tag patch]]
 
     #!/usr/bin/perl
     package IkiWiki::Plugin::tmplvars;