Fix typo/spelling (CryptozombiesHQ#529)

fa/14/09.md

@@ -90,7 +90,7 @@ Great job, you've computed the request `id`.
 
 Next, you would want to implement a simple system that keeps tracks of pending requests. Just like you did for the caller contract, for this you'll be using a mapping. This time let's call it `pendingRequests`.
 
-The `getLatestEthPrice` function should also fire and event and, lastly, it should return the request `id`.
+The `getLatestEthPrice` function should also fire an event and, lastly, it should return the request `id`.
 
 Let's see how you can implement this in code.