Removed overly-clever syntax
Removed overly-clever syntax

Summary: When running `make subperseus` I ran into a problem where
my version of make didn't seem to use full bash syntax. Therefore,
the line `mv build/node-perseus.js{,.tmp}` failed. I have removed
the clever syntax in favor of something more readable and compatible
with more shells (specifically sh syntax)

Test Plan:
-Run make subperseus and see that everything is happy

Auditors: emily, johnsullivan

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