Backslash not working

Hi,

I was just updating the test rules in PR #13 and it seems like the [backslash rule](https://github.com/SimpleRegex/Test-Rules/blob/594659ac8f9e1623fa5576447befe3d4616fc74f/backslash.rule) fails:

https://travis-ci.org/SimpleRegex/SRL-JavaScript/builds/264277712?utm_source=github_status&utm_medium=notification