use xenial

Author: juancarlostong

.travis.yml

@@ -1,4 +1,5 @@
 language: python
+
 python:
   - "2.7"
   - "3.4"
@@ -7,6 +8,7 @@ python:
   - "3.7"
   - "pypy"
   - "pypy3"
+
 install: "pip install -r requirements/core.txt;pip install -r requirements/test.txt"
 before_script: "pep8"
 addons:
@@ -22,7 +24,7 @@ stages:
 
 jobs:
   include:
-    - stage: 'Integration tests'
+    - stage: 'Trigger Integration tests'
       env: SDK=python
       language: python
       before_install: skip
@@ -33,3 +35,7 @@ jobs:
       script:
         - "ci/trigger_fullstack-sdk-compat.sh"
       after_success: skip
+
+    - stage: 'Unit tests'
+      if: TRAVIS_PYTHON_VERSION =~ /^3.7/
+      dist: xenial