Fix incorrect path in theme build script

`buildThemes.ts` had an incorrect path for generating the theme json files.

It probably happened when we did some reorganization of the styles directory.

Co-Authored-By: gibusu <95764254+gibusu@users.noreply.github.com>

styles/src/buildThemes.ts

@@ -10,7 +10,7 @@ for (let theme of themes) {
   let styleTree = snakeCase(app(theme));
   let styleTreeJSON = JSON.stringify(styleTree, null, 2);
   let outPath = path.resolve(
-    `${__dirname}/../assets/themes/${theme.name}.json`
+    `${__dirname}/../../assets/themes/${theme.name}.json`
   );
   fs.writeFileSync(outPath, styleTreeJSON);
   console.log(`- ${outPath} created`);