Upgrade to TestNG 6.5.2

The Spring TestContext Framework (TCF) currently builds against TestNG
5.10. Thus in order to ensure that the TCF builds against the latest
release of TestNG without issues and in order to investigate the
possibility of integrating with newer TestNG features, we are upgrading to
version 6.5.2.

Note, however, that the Gradle build currently does not execute any TestNG
tests; this will be addressed in SPR-9398.

Issue: SPR-8221

build.gradle

@@ -424,7 +424,7 @@ project('spring-test') {
     dependencies {
         compile project(":spring-webmvc-portlet")
         compile("javax.activation:activation:1.0", provided)
-        compile("org.testng:testng:5.10:jdk15", optional)
+        compile("org.testng:testng:6.5.2", optional)
         compile("junit:junit:4.10", optional)
         compile("javax.servlet:servlet-api:2.5", provided)
         testCompile "org.slf4j:slf4j-jcl:1.5.3"