removed a stray ] in the sample source code

In the README file, at line 193, at the end there is a stray ] which I removed, nothing major :)

README.md

@@ -190,7 +190,7 @@ RKObjectRequestOperation *operation = [[RKObjectRequestOperation alloc] initWith
 	NSLog(@"Mapped the article: %@", article);
 } failure:^(RKObjectRequestOperation *operation, NSError *error) {
 	NSLog(@"Failed with error: %@", [error localizedDescription]);
-}];]
+}];
 ```
 
 ### Managed Object Request