add reference to Spring Framework's code style in CONTRIBUTING.md

Author: fmbenhassine

CONTRIBUTING.md

@@ -95,20 +95,9 @@ This command, will provide the following output, which in this case shows a nice
 ````
 If you see intersecting lines, that usually means that you forgot to rebase you branch. As mentioned earlier, **please rebase against master** before issuing a pull request.
 
-## Mind the whitespace
-
-Please carefully follow the whitespace and formatting conventions already present in the framework.
-
-1. Tabs, not spaces
-2. Unix (LF), not DOS (CRLF) line endings
-3. Eliminate all trailing whitespace
-4. Wrap Javadoc at 90 characters
-5. Aim to wrap code at 90 characters, but favor readability over wrapping
-6. Preserve existing formatting; i.e. do not reformat code for its own sake
-7. Search the codebase using `git grep` and other tools to discover common
-   naming conventions, etc.
-8. Latin-1 (ISO-8859-1) encoding for Java sources; use `native2ascii` to convert
-   if necessary
+## Code style
+
+Please carefully follow the same [code style as Spring Framework](https://github.com/spring-projects/spring-framework/wiki/Code-Style).
 
 ## Add Apache license header to all new classes