chore(deps): bump org.jfree:jfreechart from 1.5.5 to 1.5.6

Bumps [org.jfree:jfreechart](https://github.com/jfree/jfreechart) from 1.5.5 to 1.5.6.
- [Release notes](https://github.com/jfree/jfreechart/releases)
- [Commits](jfree/jfreechart@v1.5.5...v1.5.6)

---
updated-dependencies:
- dependency-name: org.jfree:jfreechart
  dependency-version: 1.5.6
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

pom.xml

@@ -18,7 +18,7 @@
         <dependency>
             <groupId>org.jfree</groupId>
             <artifactId>jfreechart</artifactId>
-            <version>1.5.5</version>
+            <version>1.5.6</version>
         </dependency>
         <dependency>
             <groupId>junit</groupId>