Removed pytest-xdist

The test suite is much less IO-bound now with the local httpbin
instance (via pytest-httpbin). Therefore, paralelization is not
as helpful.

Makefile

@@ -22,8 +22,8 @@ init: uninstall-httpie
 	@echo
 
 test: init
-	@echo $(TAG)Running tests in on current Python in parallel and with coverage $(END)
-	py.test --cov ./httpie --cov ./tests -n 8 --doctest-modules --verbose ./httpie ./tests
+	@echo $(TAG)Running tests in on current Python with coverage $(END)
+	py.test --cov ./httpie --cov ./tests --doctest-modules --verbose ./httpie ./tests
 	@echo
 
 test-tox: init

requirements-dev.txt

@@ -1,6 +1,5 @@
 tox
 pytest
-pytest-xdist
 pytest-cov
 pytest-httpbin
 docutils

tox.ini

@@ -12,8 +12,7 @@ envlist = py26, py27, py34, pypy
 [testenv]
 deps =
     pytest
-    pytest-xdist
     pytest-httpbin
 
 commands =
-    py.test -n 8 --doctest-modules --basetemp={envtmpdir} {posargs:./tests ./httpie}
+    py.test --verbose --doctest-modules --basetemp={envtmpdir} {posargs:./tests ./httpie}