Try to fix #33 InaccessibleObjectException

[Treer]

Upgrade Gson to avoid [crash] Amidst has encounted an uncaught exception on the thread Thread[AWT-EventQueue-0,6,main] [crash] java.lang.reflect.InaccessibleObjectException: Unable to make field int java.awt.Color.value accessible: module java.desktop does not "opens java.awt" to unnamed module @3bf44630

This change can be tested via the following builds:

• https://github.com/Treer/Amidst-for-Minetest/releases/download/v1.4-2/amidst-minetest-v1-4-2.jar
• https://github.com/Treer/Amidst-for-Minetest/releases/download/v1.4-2/amidst-minetest-v1-4-2.exe