Fix spacing violation in webpack config
Fix spacing violation in webpack config

re: D28403. Auto-fixers were able to fix this up, thank goodness! I
would have been at it all day otherwise.

Auditors: emily

Test Plan:

`ka-lint`

learningequality/perseus,ariabuckles/perseus,ariabuckles/perseus,ariabuckles/perseus,learningequality/perseus,ariabuckles/perseus