Returns the path to the current library. If the current directory contains several libraries,
the first one found is returned.
@throws {Error} Throws an error if no library can be found.
@return {Promise(String)} A promise that resolves with the absolute path to the library
async function() {
      let {libraries} = await this.getProjectData();
      if (libraries instanceof Array && libraries.length) {
        return path.resolve(process.cwd(), libraries[0].path);
      }
      throw new qx.tool.cli.Utils.UserError("Cannot find library path - are you in the right directory?");
    }