Since php 7 isn't supported anymore, the old php 4 object construct was replaced with __construct(). Wordpress developers created a notice message so the plugin developers would change the way their plugins work (and also so it could run on next php versions). Since php 4 has long been dead, there's no reason to use this style of object construct.
How to fix?
Option 1 - not going to upgrade to newer php versions
just add
add_filter('deprecated_constructor_trigger_error', '__return_false');
to your functions.php file it will ignore those notices.
Option 2 - might upgrade to php 7 / prefer dealing with the issue rather than silencing it
If this is a third party plugin, beware that if you make the change yourself and the plugin developer releases an update then it will override your changes. Contacting the plugin developer to fix this issue will be the best option
Find the problematic plugin and change:
parent::WP_Widget
To
parent::__construct
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
