Build(deps): bump org.jfree:jfreechart from 1.5.4 to 1.5.5

Bumps [org.jfree:jfreechart](https://github.com/jfree/jfreechart) from 1.5.4 to 1.5.5.
- [Release notes](https://github.com/jfree/jfreechart/releases)
- [Commits](jfree/jfreechart@v1.5.4...v1.5.5)

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

Signed-off-by: dependabot[bot] <[email protected]>

build.gradle

@@ -68,7 +68,7 @@ dependencies {
   // https://mvnrepository.com/artifact/org.jdom/jdom2
   implementation 'org.jdom:jdom2:2.0.6.1'
   // https://mvnrepository.com/artifact/org.jfree/jfreechart
-  implementation 'org.jfree:jfreechart:1.5.4'
+  implementation 'org.jfree:jfreechart:1.5.5'
   // https://mvnrepository.com/artifact/org.openjdk.nashorn/nashorn-core
   implementation 'org.openjdk.nashorn:nashorn-core:15.4'
   // https://mvnrepository.com/artifact/org.slf4j/slf4j-api