Added missing import

Author: marcingrzejszczak

consumer_rabbit_middleware/src/test/java/com/example/ApplicationTests.java

@@ -16,6 +16,8 @@
 
 package com.example;
 
+import java.nio.charset.StandardCharsets;
+
 import java.util.HashMap;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;