Fixed Typo phrase "prefixes_will_be_disassociated"

[cclaerhout]

A "be" is missing in the phrase.

 

[Chris D]

Interestingly the same bug exists in XenForo 1.2.2 core:

thread_prefixes_will_be_disassociated

Thread prefixes belonging to this group will be disassociated, rather than deleted.

 

[Mike]

I've fixed both phrases now.