Update file-manager.js

[SeanC4]

Description

Hawkeye scanner does not run on Windows.
When certain modules run (eg: java-find-secbugs) the file-manager tries to get all files (getAllFilesSync). It replaces the filePath with a regex to produce a relative path
const relativePath = filePath.replace(this.targetRegex, '').
This doesn't work on Windows as the \ in the directory is a escape character. Reg ex fails and you end up with a path something like this:
D:\Code\D:\Code\Folder\ rather than D:\Code\Folder\

Fixes #131

Type of change

• Bug fix (non-breaking change which fixes an issue)

Toolchain

• JavaScript

How Has This Been Tested?

[Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. List any dependencies that are required for this change.]

Test Configuration: hawkeye scan

• Toolchain:
• SDK (incl. version): "^1.6.2"
• OS version: Windows 10
• Relevant links https://github.com/SeanC4/scanner-cli

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code

[felixhammerl]

This problem exists on many more places. I will create a more comprehensive change that addresses this problem in the modules as well.