Bump assertj-core from 3.8.0 to 3.11.1 in /modules/kafka (#1067)

Bumps [assertj-core](https://github.com/joel-costigliola/assertj-core) from 3.8.0 to 3.11.1.
- [Release notes](https://github.com/joel-costigliola/assertj-core/releases)
- [Commits](assertj/assertj@assertj-core-3.8.0...assertj-core-3.11.1)

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

Author: dependabot[bot]

modules/kafka/build.gradle

@@ -4,6 +4,6 @@ dependencies {
     compile project(':testcontainers')
 
     testCompile 'org.apache.kafka:kafka-clients:2.1.0'
-    testCompile 'org.assertj:assertj-core:3.8.0'
+    testCompile 'org.assertj:assertj-core:3.11.1'
     testCompile 'com.google.guava:guava:23.0'
 }