Add tox env for running mypy and add that to .travis.yml

.travis.yml

@@ -13,9 +13,10 @@ matrix:
        python: pypy-5.7.1
     -  env: TOXENV=pre-commit
        python: 3.6
+    -  env: TOXENV=mypy
+       python: 3.6
 install:
   - pip install coveralls tox
-  - if [[ $TRAVIS_PYTHON_VERSION == '3.6' ]]; then pip install mypy; fi
 script: tox
 after_success: coveralls
 cache:

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = flake8,py27,py33,py34,py35,py36,pre-commit,pypy
+envlist = flake8,py27,py33,py34,py35,py36,pre-commit,pypy,mypy
 skipsdist = true
 
 [testenv]
@@ -18,6 +18,13 @@ setenv =
 commands =
     pre-commit {posargs:run --all-files}
 
+[testenv:mypy]
+basepython=python3.6
+deps =
+    mypy
+commands =
+    mypy graphene
+
 [testenv:flake8]
 deps = flake8
 commands =