Run coverage when testing with Python 3.7

Author: Cito

tox.ini

@@ -6,7 +6,8 @@ deps =
     .[test]
 commands =
     py{27,py}: pytest graphql tests {posargs}
-    py{35,36,37,38,py3}: pytest graphql tests tests_py35 {posargs}
+    py{35,36,38,py3}: pytest graphql tests tests_py35 {posargs}
+    py{37}: pytest graphql tests tests_py35 {posargs: --cov-report=term-missing --cov=graphql}
 
 [testenv:pre-commit]
 basepython=python3.8