docs: Fix small grammatical error in redirect-and-alias (#2623)

"A redirect means when the user visits `/a`, **and** URL will be replaced by `/b`" so I replace the **and** with **the**.

<!--
Please make sure to read the Pull Request Guidelines:
https://github.com/vuejs/vue/blob/dev/.github/CONTRIBUTING.md#pull-request-guidelines
-->

docs/guide/essentials/redirect-and-alias.md

@@ -41,7 +41,7 @@ For other advanced usage, checkout the [example](https://github.com/vuejs/vue-ro
 
 ## Alias
 
-A redirect means when the user visits `/a`, and URL will be replaced by `/b`, and then matched as `/b`. But what is an alias?
+A redirect means when the user visits `/a`, the URL will be replaced by `/b`, and then matched as `/b`. But what is an alias?
 
 **An alias of `/a` as `/b` means when the user visits `/b`, the URL remains `/b`, but it will be matched as if the user is visiting `/a`.**