git gud levels breaks on Windows

```
Sahan Kumarasinghe@DESKTOP-NTS61AN MINGW64 ~/my-git-gud (master)
$ git gud levels
Traceback (most recent call last):
File "c:\users\sahan kumarasinghe\appdata\local\programs\python\python39\lib\runpy.py", line 197, in _run_module_as_main
return _run_code(code, main_globals, None,
File "c:\users\sahan kumarasinghe\appdata\local\programs\python\python39\lib\runpy.py", line 87, in _run_code
exec(code, run_globals)
File "C:\Users\Sahan Kumarasinghe\AppData\Local\Programs\Python\Python39\Scripts\git-gud.exe\__main__.py", line 7, in
File "c:\users\sahan kumarasinghe\appdata\local\programs\python\python39\lib\site-packages\gitgud\__main__.py", line 530, in main
GitGud().parse()
File "c:\users\sahan kumarasinghe\appdata\local\programs\python\python39\lib\site-packages\gitgud\__main__.py", line 524, in parse
self.command_dict[args.command](args)
File "c:\users\sahan kumarasinghe\appdata\local\programs\python\python39\lib\site-packages\gitgud\__main__.py", line 378, in handle_levels
show_skill_tree(
File "c:\users\sahan kumarasinghe\appdata\local\programs\python\python39\lib\site-packages\gitgud\user_messages\__init__.py", line 202, in show_skill_tree
display_entry(
File "c:\users\sahan kumarasinghe\appdata\local\programs\python\python39\lib\site-packages\gitgud\user_messages\__init__.py", line 170, in display_entry
print(indent + format_string.format(
File "c:\users\sahan kumarasinghe\appdata\local\programs\python\python39\lib\encodings\cp1252.py", line 19, in encode
return codecs.charmap_encode(input,self.errors,encoding_table)[0]
UnicodeEncodeError: 'charmap' codec can't encode characters in position 0-2: character maps to
Levels in the current skill "intro" :

0. Introduction (intro)
```

This breaks on Git Gud versions 0.3.1 and 0.4.0. Just installed git gud and git bash. Looks like it's got something to do with the elbow characters. I'll open a PR soon for a quick fix.