$XDG_CONFIG_HOME should default to ~/.config

Ref: https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html

$XDG_CONFIG_HOME defines the base directory relative to which user specific configuration files should be stored. If $XDG_CONFIG_HOME is either not set or empty, a default equal to $HOME/.config should be used.

Atm, that does not work — my XDG_CONFIG_HOME is not overriden (i.e. is unset), I have a config at ~/.config/ncurc, and git-node still complains.

从 git-node 的配置查找开始，跟踪未设置的 XDG_CONFIG_HOME 是如何处理的。将该行为与所引用的 basedir 规范以及现有的 ~/.config/ncurc 示例进行比较；完成标准是：在该变量未设置时，git-node 能识别该配置，并且不再报错。