Added Python 3.7 to Travis CI

.travis.yml

@@ -13,6 +13,8 @@ matrix:
             python: 3.6
         -   env: TOXENV=pypy
             python: pypy2.7-5.10.0
+        -   env: TOXENV=py37
+            python: 3.7-dev
 install: pip install coveralls tox
 script: tox
 before_install:

setup.py

@@ -41,7 +41,7 @@ setup(
         'cfgv>=1.0.0',
         'identify>=1.0.0',
         'nodeenv>=0.11.1',
-        'pyyaml',
+        'pyyaml>=4.2b4',
         'six',
         'toml',
         'virtualenv',

tox.ini

@@ -1,7 +1,7 @@
 [tox]
 project = pre_commit
 # These should match the travis env list
-envlist = py27,py35,py36,pypy
+envlist = py27,py35,py36,py37,pypy
 
 [testenv]
 deps = -rrequirements-dev.txt