Shortcodes should return not echo

Hi, thanks for the simple plugin.

It works great, apart from one problem: your functions echo instead of return.

http://codex.wordpress.org/Function_Reference/add_shortcode#Notes
Note that the function called by the shortcode should never produce output of any kind. Shortcode functions should return the text that is to be used to replace the shortcode.

Could this please be fixed?

Thank you.

https://wordpress.org/plugins/logout-button/