Use LOCALAPPDATA for system cache on windows

Author: Jesse Bakker

lib/src/system_cache.dart

@@ -35,8 +35,13 @@ class SystemCache {
     if (Platform.environment.containsKey('PUB_CACHE')) {
       return Platform.environment['PUB_CACHE'];
     } else if (Platform.isWindows) {
+      // If a cache dir already exists in %APPDATA%, use it, else default to %LOCALAPPDATA%
       var appData = Platform.environment['APPDATA'];
-      return p.join(appData, 'Pub', 'Cache');
+      var appDataCacheDir = p.join(appData, 'Pub', 'Cache');
+      if (Directory(appDataCacheDir).existsSync())
+        return appDataCacheDir;
+      var localAppData = Platform.environment['LOCALAPPDATA'];
+      return p.join(localAppData, 'Pub', 'Cache');
     } else {
       return '${Platform.environment['HOME']}/.pub-cache';
     }