Updated appveyor configuration

.appveyor.yml

@@ -4,11 +4,9 @@ os:
   - Visual Studio 2013
   - Visual Studio 2015
 
-matrix:
-  - vc_arch: amd64
-    target_arch: x86_64
-  - vc_arch: amd64_x86
-    target_arch: x86
+platform:
+  - x86
+  - x86_64
 
 build_script:
 - md build_pure_11