Test Python 3.7 on Travis CI

.travis.yml

@@ -8,6 +8,19 @@ python:
 env:
     - TEST_SERVER_MODE=false
     - TEST_SERVER_MODE=true
+# Due to incomplete Python 3.7 support on Travis CI (
+# https://github.com/travis-ci/travis-ci/issues/9815),
+# using a matrix is necessary
+matrix:
+  include:
+    - python: 3.7
+      env: TEST_SERVER_MODE=false
+      dist: xenial
+      sudo: true
+    - python: 3.7
+      env: TEST_SERVER_MODE=true
+      dist: xenial
+      sudo: true
 before_install:
   - export BOTO_CONFIG=/dev/null
 install: