Test Python 3.7 on Travis CI (#366)

* Test Python 3.7 on Travis CI

* feat: set os code

* feat: clean code

* feat: set dist

.travis.yml

@@ -1,17 +1,20 @@
+dist: xenial
+sudo: required
 language: python
 
-# Use container-based infrastructure
-sudo: false
-
 matrix:
   include:
     - env: TOX_ENV=py27-cryptography
+      dist: trusty
       python: 2.7
     - env: TOX_ENV=py27-pycrypto
+      dist: trusty
       python: 2.7
     - env: TOX_ENV=py34-cryptography
+      dist: trusty
       python: 3.4
     - env: TOX_ENV=py34-pycrypto
+      dist: trusty
       python: 3.4
     - env: TOX_ENV=py35-cryptography
       python: 3.5
@@ -21,10 +24,13 @@ matrix:
       python: 3.6
     - env: TOX_ENV=py36-pycrypto
       python: 3.6
+    - env: TOX_ENV=py37-cryptography
+      python: 3.7
+    - env: TOX_ENV=py37-pycrypto
+      python: 3.7
     - env: TOX_ENV=pypy-cryptography
+      dist: trusty
       python: "pypy-5.3.1"
-    # - env: TOX_ENV=pypy-pycrypto
-    # python: "pypy-5.3.1"
 
 services:
   - redis-server

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = {py27,py34,py35,py36,pypy,pypy3}-{cryptography,pycrypto}
+envlist = {py27,py34,py35,py36,py37,pypy,pypy3}-{cryptography,pycrypto}
 
 [testenv]
 usedevelop = True
@@ -8,6 +8,7 @@ basepython =
     py34: python3.4
     py35: python3.5
     py36: python3.6
+    py37: python3.7
     pypy: pypy
     pypy3: pypy3
 deps = 
@@ -39,6 +40,12 @@ extras=cryptography
 [testenv:py36-pycrypto]
 extras=pycrypto
 
+[testenv:py37-cryptography]
+extras=cryptography
+
+[testenv:py37-pycrypto]
+extras=pycrypto
+
 [testenv:pypy-cryptography]
 extras=cryptography