Speed up flake8 by skipping two irrelevant directories
diff --git a/tox.ini b/tox.ini
index 96a175f..272f5b5 100644
--- a/tox.ini
+++ b/tox.ini
@@ -85,7 +85,7 @@
     py.test --capture=no --strict --random {posargs}
 
 [flake8]
-exclude = .tox,*.egg
+exclude = .tox,*.egg,.git,_build
 select = E,W,F,N,I
 application-import-names = cryptography,cryptography_vectors,tests