class="current" in menu

Look 3 screenshots for you

http://yadi.sk/d/yBPyqrs1MANFe
http://yadi.sk/d/ydwn3_JvMAMQi
http://yadi.sk/d/jABESz87MAMg4

need change in admin.php

$links[] = '<a href="' . admin_url( 'admin.php?page=akismet-key-config' ) . '">'.__( 'Settings' ).'</a>';

to

$links[] = '<a href="' . admin_url( 'plugins.php?page=akismet-key-config' ) . '">'.__( 'Settings' ).'</a>';

https://wordpress.org/plugins/akismet/