Update CONTRIBUTING.md to indicate Gradle >= 4.3 is required (#27980)

Relates #27885.

Author: softwaredoug

CONTRIBUTING.md

@@ -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