Small issue: mk_excerpt echoing an excerpt instead of returning it

Hi there!

I recently ran into an issue with your theme, as highlighted here:
https://wordpress.org/support/topic/jetpack-sharing-options-gets-displayed-twice

The problem seems to be caused by the mk_excerpt function. It is set to echo a custom excerpt. However, you should always return and not echo when using filters.

Here are a few examples of functions hooked into filters:
https://codex.wordpress.org/Function_Reference/the_excerpt#Control_Excerpt_Length_using_Filters

The following fix appears to solve the problem:
http://i.wpne.ws/d5oU

Thanks!