Don't used pytest-xdist with setup.py test

appveyor.yml

@@ -5,7 +5,6 @@ branches:
 install:
   - ps: (new-object net.webclient).DownloadFile('https://raw.github.com/pypa/pip/master/contrib/get-pip.py', 'C:\get-pip.py')
   - C:\Python27\python.exe c:\get-pip.py
-  - C:\Python27\Scripts\pip.exe install -e .
 build: off
 test_script:
   - C:\Python27\Scripts\pip.exe --version

setup.py

@@ -11,7 +11,7 @@ class PyTest(TestCommand):
         TestCommand.finalize_options(self)
         self.test_suite = True
         self.test_args = [
-            '--doctest-modules', '-n', '8',
+            '--doctest-modules',
             './httpie', './tests'
         ]
         self.test_suite = True
@@ -23,7 +23,6 @@ class PyTest(TestCommand):
 
 tests_require = [
     'pytest',
-    'pytest-xdist',
 ]