Focus on what you're looking for, why you think the new opportunity fits, and not so much why you're leaving your current position.
I just went through a huge (pretty successful) job search in Nov.-Jan., and I used the above tactic.
FWIW, the job that turned out to be the best fit (and the one I ended up taking), was one that I talked about both personal and professional reasons.
It was something like, "I've been doing x for 15 years, but doing volunteer work in y, and I see my professional growth in that direction, which I think aligns perfectly with this position. Also, on a personal note, I just had a baby, so the idea of (in this case) stepping down / sideways in my career for a while really appeals to me and fits where I am in my life right now."
Anyway, I wanted to be a whole person in the interview, and figured that if that answer turned them off, it wouldn't be a good fit anyway.
What I didn't say: "Yeah, I returned from maternity leave to a batshit new boss who makes it impossible to balance my family demands, and I'm sick of putting out the fires he causes."