Invalidate session when operation is finished

From documentation:

The session object keeps a strong reference to the delegate until your app exits or explicitly invalidates the session. If you do not invalidate the session by calling the invalidateAndCancel or finishTasksAndInvalidate method, your app leaks memory until it exits.

XCDYouTubeKit/XCDURLGetOperation.m

@@ -95,6 +95,7 @@ - (void)finish
 {
 	self.isExecuting = NO;
 	self.isFinished = YES;
+	[self.session invalidateAndCancel];
 }
 
 #pragma mark -