[Java] Improve gradle build file to reduce warnings.
[Java] Improve gradle build file to reduce warnings.

EvilMcJerkface/Aeron,real-logic/Aeron,EvilMcJerkface/Aeron,real-logic/Aeron,mikeb01/Aeron,mikeb01/Aeron,EvilMcJerkface/Aeron,mikeb01/Aeron,EvilMcJerkface/Aeron,real-logic/Aeron,real-logic/Aeron,mikeb01/Aeron