Problem with "Custom button" feature

Hello!

I want to use custom set of buttons. What I do:

1) Select radio “Custom button” in basic settings
2) Go to https://www.addthis.com/get/sharing , choose the set and style I want, get code:

<!-- AddThis Button BEGIN -->
<div class="addthis_toolbox addthis_default_style addthis_16x16_style">
<a class="addthis_button_facebook"></a>
<a class="addthis_button_vk"></a>
<a class="addthis_button_odnoklassniki_ru"></a>
<a class="addthis_button_twitter"></a>
<a class="addthis_button_google_plusone_share"></a>
<a class="addthis_button_compact"></a><a class="addthis_counter addthis_bubble_style"></a>
</div>
<script type="text/javascript">var addthis_config = {"data_track_addressbar":true};</script>
<script type="text/javascript" src="//s7.addthis.com/js/300/addthis_widget.js#pubid=ra-51f6acb90dd7263c"></script>
<!-- AddThis Button END -->

3) Return to wp admin area, paste whole code to box, save

The problem that saving cuts “<script>” tags and code transforms to:

<!-- AddThis Button BEGIN -->
<div class="addthis_toolbox addthis_default_style addthis_16x16_style">
<a class="addthis_button_facebook"></a>
<a class="addthis_button_vk"></a>
<a class="addthis_button_odnoklassniki_ru"></a>
<a class="addthis_button_twitter"></a>
<a class="addthis_button_google_plusone_share"></a>
<a class="addthis_button_compact"></a><a class="addthis_counter addthis_bubble_style"></a>
</div>
var addthis_config = {"data_track_addressbar":true};

<!-- AddThis Button END -->

Please mind standalone line in the end of the code:

var addthis_config = {"data_track_addressbar":true};

It is the part of cut <script> tags.

Not sure if these two <script> lines are important, but I can’t keep them after saving.

https://www.ads-software.com/plugins/addthis/