docs(plugins/isocalendar): fix example

Author: lowlighter

source/plugins/isocalendar/metadata.yml

@@ -2,7 +2,7 @@ name: "📅 Isometric commit calendar"
 category: github
 description: This plugin displays an isometric view of your commit calendar along with a few additional statistics like current streak and average number of commit per day.
 examples:
-  full year calendar: https://github.com/lowlighter/lowlighter/blob/master/metrics.plugin.isocalendar.fullyear.svg
+  +full year calendar: https://github.com/lowlighter/lowlighter/blob/master/metrics.plugin.isocalendar.fullyear.svg
   half year calendar: https://github.com/lowlighter/lowlighter/blob/master/metrics.plugin.isocalendar.svg
 index: 0
 supports: