Update CONTRIBUTING.md to indicate Gradle >= 4.3 is required
Relates
@@ -94,7 +94,7 @@ Contributing to the Elasticsearch codebase
Make sure you have [Gradle](http://gradle.org) installed, as
Elasticsearch uses it as its build system. Gradle must be at least
-version 3.3 in order to build successfully.
+version 4.3 in order to build successfully.
Eclipse users can automatically configure their IDE: `gradle eclipse`
then `File: Import: Existing Projects into Workspace`. Select the
