Drop Python 3.6 environment because it's not available in Circle

Rami Chowdhury · Rami Chowdhury · commit 58e74d82329b · 2019-07-19T11:46:31.000-04:00
diff --git a/tox.ini b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = pre-commit,py{36,37}
+envlist = pre-commit,py37
 isolated_build = true
 
 [testenv]
