WordPress 4.3 Compatibility

The construct method WP_Widget has been deprecated since WP version 4.3.0, use method __construct instead in DWQA_Related_Question_Widget class on line 12

class DWQA_Related_Question_Widget extends WP_Widget {

	/**
	 * Constructor
	 *
	 * @return void
	 **/
	function DWQA_Related_Question_Widget() {
		$widget_ops = array( 'classname' => 'dwqa-widget dwqa-related-questions', 'description' => __( 'Show a list of questions that related to a question. Just show in single question page', 'dwqa' ) );
		$this->WP_Widget( 'dwqa-related-question', __( 'DWQA Related Questions', 'dwqa' ), $widget_ops );
	}

And the construct method DWQA_Related_Question_Widget also need to be changed to __construct.

https://wordpress.org/plugins/dw-question-answer/