drop Python 3.4 from appveyor.yml, add Python 3.7

Author: grlee77

appveyor.yml

@@ -7,13 +7,12 @@
 
 environment:
   matrix:
-    - PYTHON: "C:\\Python34"
-    - PYTHON: "C:\\Python34-x64"
-      DISTUTILS_USE_SDK: "1"
     - PYTHON: "C:\\Python35"
     - PYTHON: "C:\\Python35-x64"
     - PYTHON: "C:\\Python36"
     - PYTHON: "C:\\Python36-x64"
+    - PYTHON: "C:\\Python37"
+    - PYTHON: "C:\\Python37-x64"
 
 build: off