Force flake8 to use single process in xdist setup

Author: David Conner

.flake8

@@ -3,5 +3,6 @@ exclude=.git, build, install, log, dist
 extend-ignore = A005,B008,B902,C816,D100,D101,D102,D103,D104,D105,D106,D107,D203,D212,D404,I202, W503
 import-order-style = google
 max-line-length = 130
+jobs = 1
 show-source = true
 statistics = true