All forward slashes in spec output converted to backslashes

[50Wliu]

Prerequisites

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Description

A regression from #13825 is causing all forward slashes in spec output to be converted to Windows-style. For example:

Steps to Reproduce

1. Create a test that will have forward slashes in its output if it fails
2. Run that spec in the Spec Reporter on Windows and make sure it fails

Expected behavior: Forward slashes to remain forward slashes

Actual behavior: 😱 Backslashes 😱

Reproduces how often: 100%

Versions

Atom    : 1.17.0-dev-fa9092608
Electron: 1.6.4
Chrome  : 56.0.2924.87
Node    : 7.4.0

[lock]

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