Change color_no_updates to None to default to i3bar color
Change color_no_updates to None to default to i3bar color

If ``statusline`` is not set in ``~/.config/i3/config``, it defaults to
``#ffffff`` (white). Therefore, the default behavior of the updates
module in this case is to show white for both ``color_no_updates``
(system is up-to-date) and ``color_working`` (update check in progress).

However, if one sets ``statusline`` in their ``~/.config/i3/config``,
then the color will be white when the system is up-to-date, forcing the
user to manually set ``color_no_updates`` if they would prefer it match
their default i3bar color.

This commit changes the default value of ``color_no_updates`` to
``None`` so that it matches the default i3bar unless overridden.

asmikhailov/i3pystatus,facetoe/i3pystatus,asmikhailov/i3pystatus,drwahl/i3pystatus,m45t3r/i3pystatus,m45t3r/i3pystatus,facetoe/i3pystatus,schroeji/i3pystatus,ncoop/i3pystatus,teto/i3pystatus,Arvedui/i3pystatus,fmarchenko/i3pystatus,drwahl/i3pystatus,fmarchenko/i3pystatus,enkore/i3pystatus,enkore/i3pystatus,schroeji/i3pystatus,yang-ling/i3pystatus,teto/i3pystatus,richese/i3pystatus,yang-ling/i3pystatus,Arvedui/i3pystatus,ncoop/i3pystatus,eBrnd/i3pystatus,eBrnd/i3pystatus,richese/i3pystatus