[FIX] handle threads as int and use f-typing to append it to cmd

[treee111]

This PR…

• fixes TypeError: can only concatenate str (not "int") to str #143
• handles the threads variable consistent as integer and adds it via f-typing to the cmd command later on

Considerations and implementations

• the variable threads was handled as string or as int depending on whether the if-statement was run throught or not.
  

  wahooMapsCreator/wahoomc/osm_maps_functions.py

  Lines 646 to 648 in 1b5f89f

  	threads = str(multiprocessing.cpu_count() - 1)
  	if int(threads) < 1:
  	threads = 1

• if handled as integer (e.g. Windows 10 running in VirtualBox), a TypeError is thrown because a integer can't be concatenated with a string this way
  

  wahooMapsCreator/wahoomc/osm_maps_functions.py

  Line 672 in 1b5f89f

  cmd.append('threads=' + threads)

How to test

1. run this branch of wahooMapsCreator for a small country on Windows 10 in VirtualBox: python -m wahoomc cli -co malta
2. I created a alpha version, can also tested with v2.1.0a5: pip install wahoo_mc==2.1.0a5

Pull Request Checklist

• Reviewed the Contributing Guidelines
  • Especially the Pull-Requests section
• Commits (and commit-messages) are understandable
• Tested with macOS / Linux
• Tested with Windows
• Windows 10 in VirtualBox

[zenziwerken]

No more error thrown. Version 2.1.0a5 works