Bump spring-core from 5.3.12 to 5.3.20 in /nakadi-producer

Bumps [spring-core](https://github.com/spring-projects/spring-framework) from 5.3.12 to 5.3.20.
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](spring-projects/spring-framework@v5.3.12...v5.3.20)

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

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

nakadi-producer/pom.xml

@@ -86,7 +86,7 @@
         <dependency>
             <groupId>org.springframework</groupId>
             <artifactId>spring-core</artifactId>
-            <version>5.3.12</version>
+            <version>5.3.20</version>
         </dependency>
         <dependency>
             <groupId>org.mockito</groupId>