Fixed accessing AppKit element from background thread.

When forking a new code snippet repo (Plug-ins -> Configure snippets
repo) when checking the console logs AppKit outputs the following entry:

NSAlert is being used from a background thread, which is not safe.
This is probably going to crash sometimes. Break on void
_NSAlertWarnUnsafeBackgroundThreadUsage() to debug.  This will be
logged only once.  This may break in the future.

Author: clementpadovani

ACCodeSnippetRepository/Controllers/ACCodeSnippetRepositoryConfigurationWindowController.m

@@ -120,8 +120,10 @@ - (IBAction)forkRemoteRepositoryAction:(id)sender {
                         [weakSelf.window endSheet:weakSelf.progressPanel];
                         [weakSelf.progressIndicator stopAnimation:weakSelf];
                     });
-                    
-                    [weakSelf importUserSnippetsAction:weakSelf];
+				 
+				 dispatch_async(dispatch_get_main_queue(), ^{
+					[weakSelf importUserSnippetsAction:weakSelf];
+				 });
                 });
 
                 break;