Try (again) to fix issue installing mapMCDA due to DLL of deldir not found on i386.

https://github.com/krlmlr/r-appveyor#using-a-64-bit-r-installation

appveyor.yml

@@ -13,7 +13,10 @@ install:
 cache:
   - C:\RLibrary
 
+platform: x64
+
 environment:
+  R_ARCH: x64
   NOT_CRAN: true
   # env vars that may need to be set, at least temporarily, from time to time
   # see https://github.com/krlmlr/r-appveyor#readme for details