Makefile: re-add commit hash to perseus-0.js
Makefile: re-add commit hash to perseus-0.js

Summary:
I forgot to use the perseus-0.js variable instead of perseus.js
for perseus' Makefile header text. This corrects that so it gets
the appropriate header text

Test Plan:
make build; examine build/perseus-0.js

Auditors: alex

ariabuckles/perseus,iamchenxin/perseus,alexristich/perseus,abe4mvp/perseus,chirilo/perseus,junyiacademy/perseus,sachgits/perseus,ariabuckles/perseus,daukantas/perseus,iamchenxin/perseus,daukantas/perseus,abe4mvp/perseus,learningequality/perseus,ariabuckles/perseus,learningequality/perseus,junyiacademy/perseus,huangins/perseus,alexristich/perseus,huangins/perseus,ariabuckles/perseus,chirilo/perseus,sachgits/perseus