try Python 3.7 to see if MSVC 10.0 compilation errors in python/typed_ast go

away

Author: Vladimir Kotal

appveyor.yml

@@ -4,7 +4,7 @@ environment:
   MAVEN_VERSION: 3.6.0
   matrix:
     - JAVA_HOME: C:\Program Files\Java\jdk1.8.0
-      PYTHON: C:\Python34
+      PYTHON: C:\Python37
 install:
   - ps: |
       Add-Type -AssemblyName System.IO.Compression.FileSystem