Bump org.apache.dubbo:dubbo from 2.7.3 to 2.7.21

Bumps [org.apache.dubbo:dubbo](https://github.com/apache/dubbo) from 2.7.3 to 2.7.21.
- [Release notes](https://github.com/apache/dubbo/releases)
- [Changelog](https://github.com/apache/dubbo/blob/3.2/CHANGES.md)
- [Commits](https://github.com/apache/dubbo/compare/dubbo-2.7.3...dubbo-2.7.21)

---
updated-dependencies:
- dependency-name: org.apache.dubbo:dubbo
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/pom.xml b/pom.xml
index e5a9933..36461c7 100644
--- a/pom.xml
+++ b/pom.xml
@@ -20,7 +20,7 @@
 		<slf4j.version>1.7.26</slf4j.version>
 		<log4j.version>1.2.17</log4j.version>
 		<curator.version>2.12.0</curator.version>
-		<dubbo.version>2.7.3</dubbo.version>
+		<dubbo.version>2.7.21</dubbo.version>
 	</properties>
 
 	<dependencyManagement>