refactor: use shell=True on subproccess call only on nt systems

should fix linux usage

src/cli.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python3
+
 import os
 from sys import exit
 

src/main.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python3
+
 from flask import Flask
 from flask import render_template, send_file, abort
 from flaskwebgui import FlaskUI  # import FlaskUI