Merge pull request #3901 from leburgeon/patch-5

Update part9c.md

Author: mluukkai

src/content/9/en/part9c.md

@@ -1439,7 +1439,7 @@ const toNewDiaryEntry = (object: unknown): NewDiaryEntry => {
 
 If the guard does not evaluate to true, an exception is thrown.
 
-The use of the operator *in* actually now guarantees that the fields indeed exist in the object. Because of that, the existence check in parsers is no more needed:
+The use of the operator *in* actually now guarantees that the fields indeed exist in the object. Because of that, the existence checks in the parsers are no longer needed:
 
 ```js
 const parseVisibility = (visibility: unknown): Visibility => {