typo in storage message

Test Plan:
I didn't put any skill points in spelling since I need
combat skills to survive in a nuclear wasteland, but spell check says
this is better.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D14522