Added py37 (#772)

* Added py37 to travis

* Added py37 trove classifier

* Added py37 to tox
diff --git a/.travis.yml b/.travis.yml
index 60731be..cac7107 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -28,6 +28,10 @@
     env: TOXENV=py35
   - python: "3.6"
     env: TOXENV=py36
+  - python: "3.7"
+    env: TOXENV=py37
+    dist: xenial
+    sudo: true
   - python: "pypy"
     env: TOXENV=pypy
   - python: "pypy3"
@@ -42,6 +46,10 @@
     env: TOXENV=py35-cryptographyMaster
   - python: "3.6"
     env: TOXENV=py36-cryptographyMaster
+  - python: "3.7"
+    env: TOXENV=py37-cryptographyMaster
+    dist: xenial
+    sudo: true
   - python: "pypy"
     env: TOXENV=pypy-cryptographyMaster
   - python: "pypy3"
@@ -56,6 +64,10 @@
     env: TOXENV=py35-cryptographyMinimum
   - python: "3.6"
     env: TOXENV=py36-cryptographyMinimum
+  - python: "3.7"
+    env: TOXENV=py37-cryptographyMinimum
+    dist: xenial
+    sudo: true
   - python: "pypy"
     env: TOXENV=pypy-cryptographyMinimum
   - python: "pypy3"
@@ -89,6 +101,7 @@
   - env: TOXENV=py34-cryptographyMaster
   - env: TOXENV=py35-cryptographyMaster
   - env: TOXENV=py36-cryptographyMaster
+  - env: TOXENV=py37-cryptographyMaster
   - env: TOXENV=pypy-cryptographyMaster
   - env: TOXENV=pypy3-cryptographyMaster
 
diff --git a/setup.py b/setup.py
index 5e80f0c..29c11f4 100755
--- a/setup.py
+++ b/setup.py
@@ -82,6 +82,7 @@
             'Programming Language :: Python :: 3.4',
             'Programming Language :: Python :: 3.5',
             'Programming Language :: Python :: 3.6',
+            'Programming Language :: Python :: 3.7',
 
             'Programming Language :: Python :: Implementation :: CPython',
             'Programming Language :: Python :: Implementation :: PyPy',
diff --git a/tox.ini b/tox.ini
index 48cd08e..eda9e4e 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = {pypy,pypy3,py27,py34,py35,py36}{,-cryptographyMaster,-cryptographyMinimum},py27-twistedMaster,pypi-readme,check-manifest,flake8,docs,coverage-report
+envlist = {pypy,pypy3,py27,py34,py35,py36,py37}{,-cryptographyMaster,-cryptographyMinimum},py27-twistedMaster,pypi-readme,check-manifest,flake8,docs,coverage-report
 
 [testenv]
 whitelist_externals =