MINOR: Update to Gradle 2.14.1

Better performance is always welcome:

"The Gradle build itself has seen a 50% reduction in configuration time. You'll see the biggest impact on multi-project builds"

Author: Ismael Juma <ismael@juma.me.uk>

Reviewers: Ewen Cheslack-Postava <ewen@confluent.io>

Closes #1644 from ijuma/update-gradle

build.gradle

@@ -68,7 +68,7 @@ allprojects {
 }
 
 ext {
-  gradleVersion = "2.13"
+  gradleVersion = "2.14.1"
   buildVersionFileName = "kafka-version.properties"
 
   userMaxForks = project.hasProperty('maxParallelForks') ? maxParallelForks.toInteger() : null