remove --fail-under from tox (covdefaults handles this)

Committed via https://github.com/asottile/all-repos

tox.ini

diff --git a/tox.ini b/tox.ini
index 965eba9..790ce7f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -11,7 +11,7 @@
 commands =
     coverage erase
     coverage run -m pytest {posargs:tests}
-    coverage report --fail-under 100
+    coverage report
 
 [testenv:pre-commit]
 skip_install = true