Process Icon Templates
@param {string} srcFile - Path to lodash template file.
@param {string} destFile - Path to write processed file to.
@param {object} data - Data to pass to template.
@param {function} cb - Callback for when done.
function processIconTemplate(srcFile, destFile, data, cb) {
  fs.readFile(srcFile, 'utf8', (err, srcFileContents) => {
    if (err) throw err;
    const result = template(srcFileContents, {
      // Use custom template delimiters of `{{` and `}}`.
      interpolate: /{{([\s\S]+?)}}/g,
      // Use custom evaluate delimiters of `{%` and `%}`.
      evaluate: /{%([\s\S]+?)%}/g,
    })(data);
    fs.writeFile(destFile, result, cb);
  });
}