incorrect property on article.series

`article.series.series` changed to `article.series.name` so it actually shows the name.

series/Readme.md

@@ -23,7 +23,7 @@ come after them, ordered by date.
 
 The plugin provides the following variables to your templates
 
-    * `article.series.series` is the name of the series as specified in the article metadata
+    * `article.series.name` is the name of the series as specified in the article metadata
     * `article.series.index` is the index of the current article inside the series
     * `article.series.all` is an ordered list of all articles in the series (including the current one)
     * `article.series.all_previous` is an ordered list of the articles published before the current one