Python 3.7 from deadsnakes

.travis.yml

@@ -18,15 +18,16 @@ matrix:
             - python-pip
             - python2.7-dev
         ssh_known_hosts: 13.229.163.131
-    - python: 3.6
+    - python: 3.7
+      dist: xenial  # required for Python >= 3.7 (travis-ci/travis-ci#9069)
       addons:
+        sources:
+          - deadsnakes
         apt:
           packages:
             - git
-            - python3.6
-            - python3.6-pip
-            - python3.6-dev
-        ssh_known_hosts: 13.229.163.131
+            - python3.7
+         ssh_known_hosts: 13.229.163.131
 
 before_install:
   - sudo pip install -U virtualenv pre-commit pip