Fix: grammar fix in index.md (#948)

Update index.md

Fix grammar. "There's a" => "There are a"

Author: liamvgallagher

apps/svelte.dev/content/tutorial/01-svelte/02-reactivity/04-inspecting-state/index.md

@@ -6,7 +6,7 @@ It's often useful to be able to track the value of a piece of state as it change
 
 Inside the `addNumber` function, we've added a `console.log` statement. But if you click the button and open the console drawer (using the button to the right of the URL bar), you'll see a warning, and a message saying the message could not be cloned.
 
-That's because `numbers` is a reactive [proxy](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy). There's a couple of things we can do. Firstly, we can create a non-reactive _snapshot_ of the state with `$state.snapshot(...)`:
+That's because `numbers` is a reactive [proxy](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy). There are a couple of things we can do. Firstly, we can create a non-reactive _snapshot_ of the state with `$state.snapshot(...)`:
 
 ```js
 /// file: App.svelte