Adapting sample_sheets.py to Windows users

[f-marchi]

I ran into this error in trying to create sample_sheets:

File "sample_sheets.py", line 198, in create_sample_sheet
    raise ValueError(file_name_error_msg.format(idat))
ValueError: This .idat file does not have the right pattern to auto-generate a sample sheet:

To fix it for Windows users, one simply needs to change the "/" with "\\" like so:

filename = str(idat).split("\\")[-1]