Update virtualenv.rst

Author: xandfury

docs/source/installation/virtualenv.rst

@@ -1,7 +1,7 @@
 Virtualenv
 ==========
 
-A generic way to keep Python installations separate is using `virtualenv <https://pypi.python.org/pypi/virtualenv>`_. This way you can run conpot on your machine without littering your machine. This guides assumes you have Python 2 installed and running on your computer.
+A generic way to keep Python installations separate is using `virtualenv <https://pypi.python.org/pypi/virtualenv>`_. This way you can run conpot on your machine without littering your machine. This guides assumes you have Python 3.5 installed and running on your computer.
 
 
 Installation