[Java] Update Gitter badge.
[Java] Update Gitter badge.

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