build_scripts: Fix long term bug with setting self.target_platform

self.target_platform is not used anywhere outside this custom class

Author: techtonik

roundup/dist/command/build_scripts.py

@@ -60,7 +60,7 @@ def finalize_options(self):
         else:
             # default to current platform
             target = sys.platform
-        self.target_platfom = target
+        self.target_platform = target
 
         # for native builds, use current python executable path;
         # for cross-platform builds, use default executable name