Ben Gamari authored Jun 02, 2017 and Ben Gamari committed Jul 06, 2017

Otherwise this will fail if the prefix path contains spaces. Thanks to
marinelli for pointing this out.

Test Plan: Validate

Reviewers: austin

Subscribers: rwbarton, thomie

Differential Revision: https://phabricator.haskell.org/D3604

(cherry picked from commit ff363bd7)