Remove extra 10 pixel space from WordPress caption

functions.php

<?php
function my_theme_fix_extra_caption_padding( $atts ) {
	if ( ! empty( $atts['width'] ) ) {
		$atts['width'] -= 10;
	}

	return $atts;
}

add_filter( 'shortcode_atts_caption', 'my_theme_fix_extra_caption_padding' );