OWNERS: Fix 'aaronlevey' -> 'aaronlevy' typo
OWNERS: Fix 'aaronlevey' -> 'aaronlevy' typo

I can't spell.  Typo is from 49779c3e (OWNERS: Configure Prow with
approver and reviewer information, 2018-07-25, #71).

derekhiggins/installer,derekhiggins/installer