Update to Python 3.5 (GoogleCloudPlatform#534)

Change-Id: Ia42d85f7a8daba4822d8e80a52d862d992e2d364

Author: Jon Wayne Parrott

.travis.yml

@@ -19,8 +19,11 @@ env:
   - secure: TQ0e6XKeFwVkoqgOJH9f/afyRouUSC6s7LC32C4JS+O2X4sXyXTPXACmzu5wCW0BXPc6HvITMLvkf7g6XXyGlCPkjM8Uw5Vg5F9+cwN1HMlI+gK6bMGTUfrwN5ruFT+KmEnD4F93NY3xkDbZd0fw23d/mVloTc6V0gUsxEUkuhM=
 addons:
   apt:
+    sources:
+    - deadsnakes
     packages:
     - portaudio19-dev
+    - python3.5
 install:
 - pip install --upgrade pip wheel virtualenv
 - pip install nox-automation coverage

nox.py

@@ -190,7 +190,7 @@ def run_tests_in_sesssion(
             success_codes=[0, 5])  # Treat no test collected as success.
 
 
-@nox.parametrize('interpreter', ['python2.7', 'python3.4'])
+@nox.parametrize('interpreter', ['python2.7', 'python3.5'])
 def session_tests(session, interpreter):
     """Runs tests for all non-gae standard samples."""
     # session.posargs is any leftover arguments from the command line,
@@ -212,9 +212,9 @@ def session_gae(session):
 
 @nox.parametrize('subsession', ['gae', 'tests'])
 def session_travis(session, subsession):
-    """On travis, just run with python3.4 and don't run slow or flaky tests."""
+    """On travis, just run with python3.5 and don't run slow or flaky tests."""
     if subsession == 'tests':
-        interpreter = 'python3.4'
+        interpreter = 'python3.5'
         sample_directories = collect_sample_dirs(
             '.', set('./appengine/standard'))
     elif subsession == 'gae':