zsh errexit causes failed grep to exit

I noticed that my cert renewals were coming back with no output. I've managed to track it down to [line 146](https://github.com/dehydrated-io/dehydrated/blob/784fb806c891979262eef9c8f38e3c10b825aefd/dehydrated#L146). It appears that since `shwordsplit` isn't set in my environment, the grep fails, and the script exits. Turning off `errexit` for this line allows the script to continue. I do not experience this issue with Bash.