Relax requirements of setup.py

[pakal]

The setup indicates :

install_requires=['requests==2.8.1','pymongo==3.0.1','bottle==0.12.4','pytest==2.5.2','argcomplete==0.8.1']

But this makes servicemanager unusable with package managers like Poetry, in projects where other dependencies require newer versions of "requests" for example.

Maybe a ">=" would be well sufficient here ?