try to fix platform builds for `win32`

appveyor.yml

-version: 0.12.{build}
+ersion: 0.12.{build}
 
 configuration:
 - Debug
 - Release
 
-platform:
-- x86
-- x64
-
 environment:
   matrix:
   - VS_VERSION: 11
+    VS_PLATFORM: win32
+  - VS_VERSION: 11
+    VS_PLATFORM: x64
   - VS_VERSION: 12
-  - VS_VERSION: 14
-
+    VS_PLATFORM: win32
+  - VS_VERSION: 12
+    VS_PLATFORM: x64
+	
 before_build:
 - git submodule update --init --recursive
-- if "%PLATFORM%" == "x86" set PLATFORM=win32
-- cmake -H. -BBuild/VS -G "Visual Studio %VS_VERSION%" -DCMAKE_GENERATOR_PLATFORM=%PLATFORM% -DBUILD_SHARED_LIBS=true -Wno-dev
+- cmake -H. -BBuild/VS -G "Visual Studio %VS_VERSION%" -DCMAKE_GENERATOR_PLATFORM=%VS_PLATFORM% -DBUILD_SHARED_LIBS=true -Wno-dev
 
 build:
   project: Build\VS\RapidJSON.sln