Update variables-and-aliases.md (#438)

Fix typo (add 'modules')

source/guides/core-concepts/variables-and-aliases.md

@@ -24,7 +24,7 @@ Once you get the hang of async code - you'll realize you can do everything you c
 This guide explores many common patterns for writing good Cypress code that can handle even the most complex situations.
 {% endnote %}
 
-Asynchronous API's are here to stay in JavaScript. They are found everywhere in modern code. In fact, most new browser API's are asynchronous and many core `Node.js` are asynchronous as well.
+Asynchronous API's are here to stay in JavaScript. They are found everywhere in modern code. In fact, most new browser API's are asynchronous and many core `Node.js` modules are asynchronous as well.
 
 The patterns we'll explore below are useful in and outside of Cypress.