Bump spring-webmvc in /demos/client-demo

Bumps [spring-webmvc](https://github.com/spring-projects/spring-framework) from 3.2.18.RELEASE to 5.2.20.RELEASE.
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](https://github.com/spring-projects/spring-framework/compare/v3.2.18.RELEASE...v5.2.20.RELEASE)

---
updated-dependencies:
- dependency-name: org.springframework:spring-webmvc
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/demos/client-demo/pom.xml b/demos/client-demo/pom.xml
index 9b0d0f3..34f4662 100644
--- a/demos/client-demo/pom.xml
+++ b/demos/client-demo/pom.xml
@@ -33,7 +33,7 @@
     <oltu.oauth2.version>1.0.3-SNAPSHOT</oltu.oauth2.version>
     <oltu.oauth2.jwt.version>1.0.4-SNAPSHOT</oltu.oauth2.jwt.version>
     <oltu.oidc.version>0.0.1-SNAPSHOT</oltu.oidc.version>
-    <org.springframework.version>3.2.18.RELEASE</org.springframework.version>
+    <org.springframework.version>5.2.20.RELEASE</org.springframework.version>
     <servlet-api.version>2.5</servlet-api.version>
     <slf4j.version>1.7.25</slf4j.version>
   </properties>