Bump test dependencies

Author: acogoluegnes

build.gradle

@@ -44,10 +44,9 @@ ext {
 	springAmqpVersion = '2.2.10.RELEASE'
 
 	// Testing
-	mockitoVersion = '3.5.10'
-	junitPlatformVersion = '1.6.2'
-	junitJupiterVersion  = '5.6.2'
-	assertjVersion = '3.17.2'
+	mockitoVersion = '3.6.28'
+	junitJupiterVersion  = '5.7.0'
+	assertjVersion = '3.18.1'
 
 	javadocLinks = ["https://docs.oracle.com/javase/7/docs/api/",
 					"https://docs.oracle.com/javaee/6/api/",