[FIX] activation of venv, when `.venv` is a file (#1054)

Some programs (ex. Emacs with auto-virtualenvwrapper package) uses
.venv file to auto-determine the virtualenv of the project. Which is
pretty handy. As well as, it doesn't make sense inside a poetry to
try to set the venv, when it is a file.

poetry/utils/env.py

@@ -188,7 +188,7 @@ class Env(object):
 
 
         if not in_venv:
         if not in_venv:
             # Checking if a local virtualenv exists
             # Checking if a local virtualenv exists
-            if (cwd / ".venv").exists():
+            if (cwd / ".venv").exists() and (cwd / ".venv").is_dir():
                 venv = cwd / ".venv"
                 venv = cwd / ".venv"
 
 
                 return VirtualEnv(venv)
                 return VirtualEnv(venv)