This installer is almost outdated.

I installed v0.4.10, and tried to update mbed-cli to latest by running `pip install -U mbed-cli`.

I had a bad feeling when installing v0.4.10 because it installer Python 2.7, and as a result `pip install -U mbed-cli` couldn't finish successfully.
```
Successfully installed PrettyTable-0.7.2 appdirs-1.4.4 backports.functools-lru-cache-1.6.1 beautifulsoup4-4.9.1 certifi-2020.6.20 chardet-3.0.4 colorama-0.4.3 fasteners-0.15 future-0.18.2 idna-2.10 intelhex-2.2.1 junit-xml-1.9 lockfile-0.12.2 mbed-cli-1.10.4 mbed-os-tools-0.0.14 monotonic-1.5 pyserial-3.4 requests-2.24.0 six-1.15.0 soupsieve-1.9.6 urllib3-1.25.9
Traceback (most recent call last):
File "c:\python27\lib\runpy.py", line 174, in _run_module_as_main
"__main__", fname, loader, pkg_name)
File "c:\python27\lib\runpy.py", line 72, in _run_code
exec code in run_globals
File "C:\Python27\Scripts\pip.exe\__main__.py", line 9, in
File "c:\python27\lib\site-packages\pip\__init__.py", line 233, in main
return command.main(cmd_args)
File "c:\python27\lib\site-packages\pip\basecommand.py", line 252, in main
pip_version_check(session)
File "c:\python27\lib\site-packages\pip\utils\outdated.py", line 102, in pip_version_check
installed_version = get_installed_version("pip")
File "c:\python27\lib\site-packages\pip\utils\__init__.py", line 838, in get_installed_version
working_set = pkg_resources.WorkingSet()
File "c:\python27\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 644, in __init__
self.add_entry(entry)
File "c:\python27\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 700, in add_entry
for dist in find_distributions(entry, True):
File "c:\python27\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 1949, in find_eggs_in_zip
if metadata.has_metadata('PKG-INFO'):
File "c:\python27\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 1463, in has_metadata
return self.egg_info and self._has(self._fn(self.egg_info, name))
File "c:\python27\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 1823, in _has
return zip_path in self.zipinfo or zip_path in self._index()
File "c:\python27\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 1703, in zipinfo
return self._zip_manifests.load(self.loader.archive)
File "c:\python27\lib\site-packages\pip\_vendor\pkg_resources\__init__.py", line 1643, in load
mtime = os.stat(path).st_mtime
WindowsError: [Error 2] 指定されたファイルが見つかりません。: 'c:\\python27\\lib\\site-packages\\mbed_cli-1.8.3-py2.7.egg'
```

Start by reproducing the v0.4.10 installation on Windows, then run `pip install -U mbed-cli` and review the Python 2.7 traceback, especially the missing mbed_cli-1.8.3-py2.7.egg path. Done means the installer and subsequent mbed-cli upgrade complete without this failure.

Written by the indexing model from the issue text.