chore: fix comment & approve cov (#1214)

lib/request.js

@@ -280,6 +280,7 @@ module.exports = {
    */
 
   get URL() {
+    /* istanbul ignore else */
     if (!this.memoizedURL) {
       const protocol = this.protocol;
       const host = this.host;
@@ -642,7 +643,7 @@ module.exports = {
    *     // => "text/plain"
    *
    *     this.get('Something');
-   *     // => undefined
+   *     // => ''
    *
    * @param {String} field
    * @return {String}
@@ -694,6 +695,8 @@ module.exports = {
  * @return {Object}
  * @api public
  */
+
+/* istanbul ignore else */
 if (util.inspect.custom) {
   module.exports[util.inspect.custom] = module.exports.inspect;
 }