OSX fixes

packages/zefyr/lib/src/widgets/__theme.dart

     String fontFamily;
     switch (themeData.platform) {
       case TargetPlatform.iOS:
+      case TargetPlatform.macOS:
         fontFamily = 'Menlo';
         break;
       case TargetPlatform.android:

packages/zefyr/lib/src/widgets/common.dart

       Color cursorColor;
       switch (theme.platform) {
         case TargetPlatform.iOS:
+        case TargetPlatform.macOS:
           cursorColor ??= CupertinoTheme.of(context).primaryColor;
           break;