Exports the cache to an external file. Note that the structure of the cache
data can change any time. Do not build anything on it. You have been warned.
@param path {String}
@return {void}
async function(path) {
      return fs.writeFileAsync(path, JSON.stringify(this.__cache, null, 2), "UTF-8")
        .catch(e => console.error(`Error exporting cache to ${path}:` + e.message));
    }