Test on Python 3.7-dev

Add Python 3.7 classifier
diff --git a/.travis.yml b/.travis.yml
index c01b079..d91198c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -18,6 +18,8 @@
       env: TOXENV=py35
     - python: 3.6
       env: TOXENV=py36
+    - python: 3.7-dev
+      env: TOXENV=py37
     - python: pypy
       env: TOXENV=pypy
 
diff --git a/setup.py b/setup.py
index 479ff04..efd12a5 100644
--- a/setup.py
+++ b/setup.py
@@ -33,6 +33,7 @@
     "Programming Language :: Python :: 3.4",
     "Programming Language :: Python :: 3.5",
     "Programming Language :: Python :: 3.6",
+    "Programming Language :: Python :: 3.7",
     "Programming Language :: Python :: Implementation :: CPython",
     "Programming Language :: Python :: Implementation :: PyPy",
     "Topic :: Software Development :: Libraries :: Python Modules",
diff --git a/tox.ini b/tox.ini
index 517dbc3..9d21df6 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = py26,py27,pypy,py33,py34,py35,py36
+envlist = py26,py27,pypy,py33,py34,py35,py36,py37
 
 [testenv]
 deps =