python-gpiozero should depend on python-pkg-resources

[m-reiter]

Importing Button from gpiozero fails if python-pkg-resources is not installed:

    from gpiozero import Button
  File "/usr/lib/python2.7/dist-packages/gpiozero/__init__.py", line 58, in <module>
    from .devices import (
  File "/usr/lib/python2.7/dist-packages/gpiozero/devices.py", line 18, in <module>
    import pkg_resources
ImportError: No module named pkg_resources

So I guess a dependency should probably be added.

[broo0ose]

I'm getting this as well on python and python3

[bennuttall]

You need to install python-dev and/or python3-dev:

sudo apt install python-dev python3-dev

[lurch]

...or you can just install python-pkg-resources and/or python3-pkg-resources :

sudo apt-get install python-pkg-resources python3-pkg-resources

(see #538 (comment) )