fix(cheerio): #attr() can be used without arguments (#20193)

types/cheerio/cheerio-tests.ts

@@ -52,6 +52,7 @@ var $multiEl = $('selector', 'selector', 'selector');
  */
 
 // attr
+$el.attr();
 $el.attr('id');
 $el.attr('id', 'favorite').html();
 

types/cheerio/index.d.ts

@@ -13,6 +13,7 @@ interface Cheerio {
 
     // Attributes
 
+    attr(): {[attr: string]: string};
     attr(name: string): string;
     attr(name: string, value: any): Cheerio;