Update to match graphql-core

Author: Daniel Gallagher

.travis.yml

@@ -1,23 +1,24 @@
 language: python
-python: 3.6
-env:  # These should match the tox env list.
-    - TOXENV=flake8
-    - TOXENV=py27
-    - TOXENV=py33
-    - TOXENV=py34
-    - TOXENV=py35
-    - TOXENV=py36
-    - TOXENV=pypy
-    - TOXENV=pre-commit
-  global:
-    secure: SQC0eCWCWw8bZxbLE8vQn+UjJOp3Z1m779s9SMK3lCLwJxro/VCLBZ7hj4xsrq1MtcFO2U2Kqf068symw4Hr/0amYI3HFTCFiwXAC3PAKXeURca03eNO2heku+FtnQcOjBanExTsIBQRLDXMOaUkf3MIztpLJ4LHqMfUupKmw9YSB0v40jDbSN8khBnndFykmOnVVHznFp8USoN5F0CiPpnfEvHnJkaX76lNf7Kc9XNShBTTtJsnsHMhuYQeInt0vg9HSjoIYC38Tv2hmMj1myNdzyrHF+LgRjI6ceGi50ApAnGepXC/DNRhXROfECKez+LON/ZSqBGdJhUILqC8A4WmWmIjNcwitVFp3JGBqO7LULS0BI96EtSLe8rD1rkkdTbjivajkbykM1Q0Tnmg1adzGwLxRUbTq9tJQlTTkHBCuXIkpKb1mAtb/TY7A6BqfnPi2xTc/++qEawUG7ePhscdTj0IBrUfZsUNUYZqD8E8XbSWKIuS3SHE+cZ+s/kdAsm4q+FFAlpZKOYGxIkwvgyfu4/Plfol4b7X6iAP9J3r1Kv0DgBVFst5CXEwzZs19/g0CgokQbCXf1N+xeNnUELl6/fImaR3RKP22EaABoil4z8vzl4EqxqVoH1nfhE+WlpryXsuSaF/1R+WklR7aQ1FwoCk8V8HxM2zrj4tI8k=
-install: pip install coveralls tox flake8 mypy
+matrix:
+  include:
+    -  env: TOXENV=py27
+    -  env: TOXENV=py34
+       python: 3.4
+    -  env: TOXENV=py35
+       python: 3.5
+    -  env: TOXENV=py36
+       python: 3.6
+    -  env: TOXENV=pypy
+       python: pypy-5.7.1
+    -  env: TOXENV=pre-commit
+       python: 3.6
+install: pip install coveralls tox mypy
 script: tox
 after_success: coveralls
 cache:
-    directories:
-        - $HOME/.cache/pip
-        - $HOME/.cache/pre-commit
+  directories:
+    - $HOME/.cache/pip
+    - $HOME/.cache/pre-commit
 deploy:
   provider: pypi
   user: syrusakbary