according to http://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.
gradle is now one of the most popular tools on linux - because of its relationship with Android. It would be awesome if you guys could follow the spec.
P.S. a similar bug has been filed on Android Studio.