Bump spring-webmvc in /samples/samples-springmvc

Bumps [spring-webmvc](https://github.com/spring-projects/spring-framework) from 4.3.21.RELEASE to 5.2.20.RELEASE.
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](spring-projects/spring-framework@v4.3.21.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>

samples/samples-springmvc/pom.xml

@@ -9,7 +9,7 @@
     <version>0.0.1-SNAPSHOT</version>
     <packaging>war</packaging>
     <properties>
-        <spring.version>4.3.21.RELEASE</spring.version>
+        <spring.version>5.2.20.RELEASE</spring.version>
         <jackson.version>2.10.0.pr1</jackson.version>
         <jetty.version>8.1.5.v20120716</jetty.version>
         <jetty.jsp.version>8.1.4.v20120524</jetty.jsp.version>