Bug fixes and improvements (#1205)

* Add Ruby code blocks to documents

* Remove Ruby code from en/docs

* Remove "center-table" class in index.md

* Add "data-toc-label" to handle the latex heading during the build process

* Use normal JD link instead.

* Bug fixes

docs/chapter_dynamic_programming/index.md

@@ -1,11 +1,7 @@
 # 动态规划
 
-<div class="center-table" markdown>
-
 ![动态规划](../assets/covers/chapter_dynamic_programming.jpg)
 
-</div>
-
 !!! abstract
 
     小溪汇入河流，江河汇入大海。