Bump assertj-core from 3.14.0 to 3.15.0 in /modules/pulsar (#2305)

Bumps [assertj-core](https://github.com/joel-costigliola/assertj-core) from 3.14.0 to 3.15.0.
- [Release notes](https://github.com/joel-costigliola/assertj-core/releases)
- [Commits](assertj/assertj@assertj-core-3.14.0...assertj-core-3.15.0)

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

modules/pulsar/build.gradle

@@ -4,5 +4,5 @@ dependencies {
     compile project(':testcontainers')
 
     testCompile group: 'org.apache.pulsar', name: 'pulsar-client', version: '2.5.0'
-    testCompile group: 'org.assertj', name: 'assertj-core', version: '3.14.0'
+    testCompile group: 'org.assertj', name: 'assertj-core', version: '3.15.0'
 }