Fix Travis build (#1)

Author: johnthagen

.travis.yml

@@ -1,15 +1,16 @@
 language: python
 
-python:
-  - 3.7
-    dist: xenial
-    sudo: true
-  - 3.6
-  - 3.5
-  - 3.4
-  - 2.7
-  - pypy
-  - pypy3
+matrix:
+    include:
+        - python: 2.7
+        - python: 3.4
+        - python: 3.5
+        - python: 3.6
+        - python: 3.7
+          dist: xenial
+          sudo: true
+        - python: pypy
+        - python: pypy3
 
 install:
   - pip install -r requirements.txt