add flake8 exclude and change coverage to 75%

tox.ini

 [tox]
 envlist = py36
 
+[flake8]
+exclude = venv,.tox
+
 [testenv]
 deps =
     coverage
@@ -9,9 +12,8 @@ deps =
 
 commands =
     coverage erase
-    coverage run --source api -m py.test {posargs}
+    coverage run --source brian_dashboard_manager -m py.test {posargs}
     coverage xml
     coverage html
-    coverage report --fail-under 85
-    flake8
-
+    coverage report --fail-under 75
+    flake8
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