added xdist to app veyor...let's see how this goes

Author: erinxocon

Diff for: Pipfile

@@ -7,7 +7,4 @@ sphinx = "<=1.5.5"
 "-e ." = "*"
 twine = "*"
 "sphinx-click" = "*"
-"pytest-xdist" = {version = "*", os_name = "=='posix'"}
-
-
-
+"pytest-xdist" = *

Diff for: appveyor.yml

@@ -52,4 +52,4 @@ install:
   - "pipenv install --system --dev --skip-lock"
 
 test_script:
-  - "pytest tests/test_pipenv.py tests/test_project.py tests/test_utils.py"
+  - "pipenv run pytest -n 8 tests/test_pipenv.py tests/test_project.py tests/test_utils.py"