👷 Travis: Use test matrix

.travis.yml

@@ -1,15 +1,13 @@
-language: python
-python:
-  - "2.6"
-    dist: trusty
-  - "2.7"
-  - "3.2"
-    dist: trusty
-  - "3.3"
-    dist: trusty
-  - "3.4"
-  - "nightly"
-sudo: false
+matrix:
+  include:
+    - python: 2.7
+    - python: 3.4
+    - python: 3.5
+    - python: 3.6
+    - python: 3.7
+      dist: xenial
+      sudo: true
+
 
 # command to run tests
 script: py.test