docs: Fix prev/next links in content section

docs/content/content/example.md

@@ -7,7 +7,7 @@ linktitle: Example
 menu:
   main:
     parent: content
-prev: /content/summaries
+prev: /content/multilingual
 next: /themes/overview
 notoc: true
 title: Example Content File

docs/content/content/markdown-extras.md

@@ -7,7 +7,7 @@ menu:
   main:
     parent: content
 prev: /content/summaries
-next: /content/example
+next: /content/multilingual
 title: Markdown Extras
 weight: 66
 toc: false

docs/content/content/multilingual.md

@@ -3,8 +3,8 @@ date: 2016-01-02T21:21:00Z
 menu:
   main:
     parent: content
+prev: /content/markdown-extras
 next: /content/example
-prev: /content/summaries
 title: Multilingual Mode
 weight: 68
 toc: true