code: function save(projectRoot, platform, version) {
      var platformsDir = path.join(projectRoot, 'platforms');
      var platformJsonFile = path.join(platformsDir, 'platforms.json');
  
      var data = {};
      if(fs.existsSync(platformJsonFile)){
          data = getJson(platformJsonFile);
      }
      data[platform] = version;
      fs.writeFileSync(platformJsonFile, JSON.stringify(data, null, 4), 'utf-8');
  }
docs: Saves platform@version into platforms.json