ci: test on Python 3.7 on AppVeyor

and drop Python 3.3 test

Author: whtsky

appveyor.yml

@@ -8,14 +8,14 @@ environment:
   matrix:
     - PYTHON: "C:\\Python27"
     - PYTHON: "C:\\Python27-x64"
-    - PYTHON: "C:\\Python33"
-    - PYTHON: "C:\\Python33-x64"
     - PYTHON: "C:\\Python34"
     - PYTHON: "C:\\Python34-x64"
     - PYTHON: "C:\\Python35"
     - PYTHON: "C:\\Python35-x64"
     - PYTHON: "C:\\Python36"
     - PYTHON: "C:\\Python36-x64"
+    - PYTHON: "C:\\Python37"
+    - PYTHON: "C:\\Python37-x64"
 
 init:
   - ps: "ls C:/Python*"