Fix possible license issue

[bachp]

Tracing back the forks I see some license problems.

• https://github.com/tfriedel/python-lightify => License file stating Apache-2.0, setup.py stating BSD
• https://github.com/aneumeier/python-lightify => License file stating Apache-2.0, setup.py stating BSD
• https://github.com/mikma/python-lightify => License file stating Apache-2.0

As the original fork by @mikma was Apache-2.0 I assume the original code was Apache-2.0.

So if all contributors agree I suggest clarifying this in putting the code completly under Apache-2.0 license.

This PR fixes this in the setup.py, please feel free to accept it if you aggree.