Removed -x option for py.test

The -x option makes py.test run failed tests first. However, tests that
failed because of interference with previous tests will be falsely marked
as PASSED when this happens.

setup.cfg

@@ -1,5 +1,5 @@
 [tool:pytest]
-addopts = -v --cov attract --cov-report term-missing --ignore node_modules -x --ff
+addopts = -v --cov attract --cov-report term-missing --ignore node_modules --ff
 
 [pep8]
 max-line-length = 100