add Python 3.7 to Travis CI test harness

Author: emmanvg

.travis.yml

@@ -7,6 +7,7 @@ python:
   - "3.4"
   - "3.5"
   - "3.6"
+  - "3.7"
 install:
   - pip install -U pip setuptools
   - pip install tox-travis

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py27, py34, py35, py36, lxml23, docs, no-maec
+envlist = py27, py34, py35, py36, py37, lxml23, docs, no-maec
 
 [testenv]
 commands =
@@ -39,3 +39,4 @@ python =
   3.4: py34, no-maec
   3.5: py35, no-maec
   3.6: py36, no-maec
+  3.7: py37, no-maec