tox/travis/appveyor: enable testing on py3.7

.appveyor.yml

@@ -18,6 +18,7 @@ environment:
     - PYTHON: "C:\\Python35-x64"
     - PYTHON: "C:\\Python36"
     - PYTHON: "C:\\Python36-x64"
+    - PYTHON: "C:\\Python37-x64"
 
 install:
   - |

.travis.yml

@@ -12,6 +12,7 @@ python:
   - "3.4"
   - "3.5"
   - "3.6"
+  - "3.7"
   - "nightly"
 install:
   - pip install -U pip tox virtualenv codecov

tox.ini

@@ -4,7 +4,7 @@
 # and then run "tox" from this directory.
 
 [tox]
-envlist = {py27,py34,py35,py36,pypy,flake8}
+envlist = {py27,py34,py35,py36,py37,pypy,flake8}
 skip_missing_interpreters = True
 minversion = 2.4.0