Bump amqp-client from 5.5.3 to 5.6.0 in /core (#1186)

Bumps [amqp-client](https://github.com/rabbitmq/rabbitmq-java-client) from 5.5.3 to 5.6.0.
- [Release notes](https://github.com/rabbitmq/rabbitmq-java-client/releases)
- [Changelog](https://github.com/rabbitmq/rabbitmq-java-client/blob/v5.6.0/release-versions.txt)
- [Commits](rabbitmq/rabbitmq-java-client@v5.5.3...v5.6.0)

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

core/build.gradle

@@ -118,7 +118,7 @@ dependencies {
     }
 
     testCompile 'redis.clients:jedis:3.0.1'
-    testCompile 'com.rabbitmq:amqp-client:5.5.3'
+    testCompile 'com.rabbitmq:amqp-client:5.6.0'
     testCompile 'org.mongodb:mongo-java-driver:3.9.1'
     testCompile ('org.mockito:mockito-core:2.23.4') {
         exclude(module: 'hamcrest-core')