Add py37 (#4298)

* test against python 3.7 for windows

* update docs to say we test on 3.7

* more succinct

* maybe make this actually work.

* link properly

* moar changes
diff --git a/Jenkinsfile b/Jenkinsfile
index 33bce2d..2697b8f 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -5,11 +5,11 @@
 def configs = [
     [
         label: 'windows',
-        toxenvs: ['py27', 'py34', 'py35', 'py36'],
+        toxenvs: ['py27', 'py34', 'py35', 'py36', 'py37'],
     ],
     [
         label: 'windows64',
-        toxenvs: ['py27', 'py34', 'py35', 'py36'],
+        toxenvs: ['py27', 'py34', 'py35', 'py36', 'py37'],
     ],
     [
         label: 'freebsd11',
@@ -152,9 +152,10 @@
                             py27: "C:\\Python27\\python.exe",
                             py34: "C:\\Python34\\python.exe",
                             py35: "C:\\Python35\\python.exe",
-                            py36: "C:\\Python36\\python.exe"
+                            py36: "C:\\Python36\\python.exe",
+                            py37: "C:\\Python37\\python.exe"
                         ]
-                        if (toxenv == "py35" || toxenv == "py36") {
+                        if (toxenv == "py35" || toxenv == "py36" || toxenv == "py37") {
                             opensslPaths = [
                                 "windows": [
                                     "include": "C:\\OpenSSL-Win32-2015\\include",