pipenv: Set environment variables via .env

Fixes #515

Author: hroncok

.env

@@ -0,0 +1 @@
+PYTHONPATH=.

Pipfile

@@ -4,9 +4,9 @@ verify_ssl = true
 name = "pypi"
 
 [scripts]
-naucse = "env PYTHONPATH=. python -m naucse"
-serve = "env PYTHONPATH=. python -m naucse serve"
-freeze = "env PYTHONPATH=. python -m naucse freeze"
+naucse = "python -m naucse"
+serve = "python -m naucse serve"
+freeze = "python -m naucse freeze"
 test = "python -m pytest test_naucse/"
 
 [packages]