Update tests.js

Author: josemoracard

exercises/02.1-Background/tests.js

@@ -11,7 +11,7 @@ describe("All the styles should be applied", ()=>{
   const link = document.querySelector("link");
   const title = document.querySelector('title');
 
-  test("The body tag should not contains any inline style", ()=>{
+  test("The body tag should not contain any inline style", ()=>{
     document.querySelector(
       "head"
     ).innerHTML = `<style>${css.toString()}</style>`;