Default log4j2.xml is suboptimal

The default log4j2.xml has a line like:

<Configuration status="WARN" packages="net.minecraft,com.mojang">

This is suboptimal as log4j will scan the entire list of these classes for handlers. Since the only handlers are in com.mojang.util, by changing the configuration to

<Configuration status="WARN" packages="com.mojang.util">

application startup speed will improve by seconds.