Move coverage configuration to the config file

.coveragerc

diff --git a/.coveragerc b/.coveragerc
index 03fc621..58a1992 100644
--- a/.coveragerc
+++ b/.coveragerc
@@ -1,5 +1,8 @@
 [run]
 branch = True
+source =
+    cryptography/
+    tests/
 
 [report]
 exclude_lines =

tox.ini

diff --git a/tox.ini b/tox.ini
index ef5e46d..98cd8a6 100644
--- a/tox.ini
+++ b/tox.ini
@@ -11,7 +11,7 @@
     pytest
     ./vectors
 commands =
-    coverage run --source=cryptography/,tests/ -m pytest --capture=no --strict {posargs}
+    coverage run -m pytest --capture=no --strict {posargs}
     coverage report -m
 
 [testenv:docs]