fix(core): lower required JNI version to 1.6
fix(core): lower required JNI version to 1.6

Version 1.8 does not add anything LWJGL needs and 1.6 is compatible
with Android.

LWJGL-CI/lwjgl3,TheMrMilchmann/lwjgl3,code-disaster/lwjgl3,LWJGL/lwjgl3,LWJGL/lwjgl3,code-disaster/lwjgl3,LWJGL/lwjgl3,LWJGL-CI/lwjgl3,TheMrMilchmann/lwjgl3,code-disaster/lwjgl3,TheMrMilchmann/lwjgl3,LWJGL-CI/lwjgl3,LWJGL-CI/lwjgl3,TheMrMilchmann/lwjgl3,code-disaster/lwjgl3,LWJGL/lwjgl3