avoid run-on paragraphs in key update reports

Without this fix, we see key update messages like this:

Please take care of these keys for list test@x.mayfirst.org.

Expires in 9 days:
0xXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX test@example.comIs expired:
0xYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY other@example.com

This avoids having each note strung together on a single line.