Fix typo, extra "s" in "session" (#958)

Author: ptaberg

docs/quickstarts/gatsby.mdx

@@ -98,7 +98,7 @@ export default function IndexPage() {
 ```
 
 
-### Read sesssion and user data
+### Read session and user data
 
 Clerk provides a set of [hooks and helpers](/docs/references/react/use-user) that you can use to access the active session and user data in your React application. Here are examples of how to use these helpers.