add Travis testing for CPython 3.6

Author: mattsb42-aws

.travis.yml

@@ -54,6 +54,17 @@ matrix:
       env: TOXENV=py35-pycrypto-norsa
     - python: 3.5
       env: TOXENV=py35-compatibility
+    # CPython 3.6
+    - python: 3.6
+      env: TOXENV=py35-base
+    - python: 3.6
+      env: TOXENV=py35-cryptography-only
+    - python: 3.6
+      env: TOXENV=py35-pycryptodome-norsa
+    - python: 3.6
+      env: TOXENV=py35-pycrypto-norsa
+    - python: 3.6
+      env: TOXENV=py35-compatibility
     # PyPy 5.3.1
     - python: pypy-5.3.1
       env: TOXENV=pypy-base
@@ -79,4 +90,4 @@ matrix:
 # matrix:
 #   include:
 #     - python: 3.6
-#       env: TOX_ENV=flake8
+#       env: TOX_ENV=flake8