Adding Python 3.7 to appveyor matrix. (#640)
Adding Python 3.7 to appveyor matrix. (#640)

* Adding Python 3.7 to appveyor matrix.

* Removing miniconda virtual environment

* Using venv module for virtual environments

* Enabling Python 3.5 and Python 3.6

QISKit/qiskit-sdk-py,QISKit/qiskit-sdk-py,QISKit/qiskit-sdk-py