Missing libffi6 when installing on Ubuntu 20.04 LTS

[IamGianluca]

Hi,

Thank you for the wonderful tool!

I've recently upgraded to Ubuntu 20.04 LTS and tried to install powerline-shell from the Git repository. This is the error message I see:

$ python setup.py install
Traceback (most recent call last):
  File "setup.py", line 2, in <module>
    from setuptools import setup, find_packages
  File "/home/gianluca/.pyenv/versions/3.8.2/lib/python3.8/site-packages/setuptools/__init__.py", line 20, in <module>
    from setuptools.dist import Distribution, Feature
  File "/home/gianluca/.pyenv/versions/3.8.2/lib/python3.8/site-packages/setuptools/dist.py", line 35, in <module>
    from setuptools import windows_support
  File "/home/gianluca/.pyenv/versions/3.8.2/lib/python3.8/site-packages/setuptools/windows_support.py", line 2, in <module>
    import ctypes
  File "/home/gianluca/.pyenv/versions/3.8.2/lib/python3.8/ctypes/__init__.py", line 7, in <module>
    from _ctypes import Union, Structure, Array
ImportError: libffi.so.6: cannot open shared object file: No such file or directory

Ubuntu 20.04 LTS doesn't have libffi6, instead, it comes with libffi7 already installed. I've tried to install libffi6 but it doesn't ship with this new version of Ubuntu.

$ sudo apt-get install libffi6
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package libffi6
$ sudo apt-get install libffi7
[sudo] password for gianluca: 
Sorry, try again.
[sudo] password for gianluca: 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
libffi7 is already the newest version (3.3-4).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

[IamGianluca]

FYI, installing via pip install powerline-shell on the same OS works.