Fixing Visual Studio (MSVC) compilation

[raphaellenain]

Thanks a lot for contributing to DGtalTools, before submitting your PR, please fill up the description and make sure that all checkboxes are checked.

PR Description

your description here

Checklist

• Doxygen documentation of the code completed (classes, methods, types, members...).
• Main tool doxygen documentation (following existing documentation of DGtalTools documentation.
• Check if it follows the tools structure described in CONTRIBUTING.md
• New entry in the ChangeLog.md added.
• Update the readme with potentially a screenshot of the tools if it applies.
• No warning raised in Debug cmake mode (otherwise, Travis C.I. will fail).

[kerautret]

Thanks @raphaellenain 👌, I just added a precision on the change in the readme.
Merging.