Loki: Correct grammar in DerivedFields.tsx (#28885)

grammarz 😉

public/app/plugins/datasource/loki/configuration/DerivedFields.tsx

@@ -33,7 +33,7 @@ export const DerivedFields = (props: Props) => {
       <h3 className="page-heading">Derived fields</h3>
 
       <div className={styles.infoText}>
-        Derived fields can be used to extract new fields from the log message and create link from it's value.
+        Derived fields can be used to extract new fields from a log message and create a link from its value.
       </div>
 
       <div className="gf-form-group">