Fix permalink to represent its current dir

Otherwise the picture cant be found, as the jekyll build process will put this file in a 'dm' directory and the other stuff like resources in a 'data-mapper' directory (because resources dont have permalink specified they are served static)

Author: markusmo3

data-mapper/index.md

@@ -2,7 +2,7 @@
 layout: pattern
 title: Data Mapper
 folder: data-mapper
-permalink: /patterns/dm/
+permalink: /patterns/data-mapper/
 categories: Persistence Tier
 tags:
  - Java