[DOCS] Update coding_guide.md
### Motivation
The link to `OrderedSafeExecutor` does not work.
### Changes
Correct the link to `OrderedExecutor`.
Reviewers: Sijie Guo <None>
This closes #2196 from Jennifer88huang/patch-1
diff --git a/site/community/coding_guide.md b/site/community/coding_guide.md
index 216cbd5..614b626 100644
--- a/site/community/coding_guide.md
+++ b/site/community/coding_guide.md
@@ -77,7 +77,7 @@
Apache BookKeeper is a low latency system. So it is implemented as a purely asynchronous service. This is accomplished as follows:
* All public classes should be **thread-safe**.
-* We prefer using [OrderedSafeExecutor](https://github.com/apache/bookkeeper/blob/master/bookkeeper-server/src/main/java/org/apache/bookkeeper/util/OrderedSafeExecutor.java) for executing any asynchronous actions. The mutations to same instance should be submitted to same thread to execute.
+* We prefer using [OrderedExecutor](https://github.com/apache/bookkeeper/blob/master/bookkeeper-common/src/main/java/org/apache/bookkeeper/common/util/OrderedExecutor.java) for executing any asynchronous actions. The mutations to same instance should be submitted to same thread to execute.
* If synchronization and locking is required, they should be in a fine granularity way.
* All threads should have proper meaningful name.
* If a class is not threadsafe, it should be annotated [@NotThreadSafe](https://github.com/misberner/jsr-305/blob/master/ri/src/main/java/javax/annotation/concurrent/NotThreadSafe.java). The instances that use this class is responsible for its synchronization.
