add Travis testing for CPython 3.7

Author: mattsb42-aws

.travis.yml

@@ -65,6 +65,29 @@ matrix:
       env: TOXENV=py35-pycrypto-norsa
     - python: 3.6
       env: TOXENV=py35-compatibility
+    # CPython 3.7
+    # xenial + sudo are currently needed to get 3.7
+    # https://github.com/travis-ci/travis-ci/issues/9815
+    - python: 3.7
+      env: TOXENV=py35-base
+      dist: xenial
+      sudo: true
+    - python: 3.7
+      env: TOXENV=py35-cryptography-only
+      dist: xenial
+      sudo: true
+    - python: 3.7
+      env: TOXENV=py35-pycryptodome-norsa
+      dist: xenial
+      sudo: true
+    - python: 3.7
+      env: TOXENV=py35-pycrypto-norsa
+      dist: xenial
+      sudo: true
+    - python: 3.7
+      env: TOXENV=py35-compatibility
+      dist: xenial
+      sudo: true
     # PyPy 5.3.1
     - python: pypy-5.3.1
       env: TOXENV=pypy-base