Fix typo that changes meaning of sentence (peak != peek) (#1046)

Author: fzyzcjy

example/lib/generic_response_class_example.dart

@@ -40,7 +40,7 @@ class BaseResponse<T> {
     } else if (json is List) {
       // NOTE: this logic assumes the ONLY valid value for a `List` in this case
       // is a List<Author>. If that assumption changes, then it will be
-      // necessary to "peak" into non-empty lists to determine the type!
+      // necessary to "peek" into non-empty lists to determine the type!
 
       return json
           .map((e) => Article.fromJson(e as Map<String, dynamic>))