Added Python 3.7 support

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index 6d428ce..2628377 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -7,6 +7,8 @@
         python: 3.5
     -   env: TOXENV=py36
         python: 3.6
+    -   env: TOXENV=py37
+        python: 3.7-dev
     -   env: TOXENV=pypy
         python: pypy-5.7.1
 install: pip install coveralls tox

setup.py

diff --git a/setup.py b/setup.py
index bc10172..c783d80 100644
--- a/setup.py
+++ b/setup.py
@@ -27,7 +27,7 @@
         # quickfix to prevent pycodestyle conflicts
         'flake8!=2.5.3',
         'autopep8>=1.3',
-        'pyyaml',
+        'pyyaml>=4.2b4',
         'six',
     ],
     entry_points={

tox.ini

diff --git a/tox.ini b/tox.ini
index 0b33d3e..d173921 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,6 +1,6 @@
 [tox]
 # These should match the travis env list
-envlist = py27,py35,py36,pypy
+envlist = py27,py35,py36,py37,pypy
 
 [testenv]
 deps = -rrequirements-dev.txt