Build Failing for openJdk7 & KafkaVer:0.10.2.0

[NNSatyaKarthik]

Here is the reference: https://travis-ci.org/mesos/kafka/jobs/264639772

Error Message :

Error resolving plugin [id: 'de.undercouch.download', version: '2.1.0']
> Could not GET 'https://plugins.gradle.org/api/gradle/2.8/plugin/use/de.undercouch.download/2.1.0'.
   > peer not authenticated

Resolution:

• Updating to gradle 4.1 and de.undercouch.download to 3.2.0 fixed to issue.

I updated build.gradle and gradle-wrapper.properties in this PR