Set session user-agent to desktop client (fixes 0xced#510)

YouTube appears to randomly redirect client to mobile site. This should fix the issue for now

XCDYouTubeKit/XCDYouTubeVideoOperation.m

@@ -89,12 +89,12 @@ - (instancetype) initWithVideoIdentifier:(NSString *)videoIdentifier languageIde
 	_videoIdentifier = videoIdentifier ?: @"";
 	_languageIdentifier = languageIdentifier ?: @"en";
 
-	_session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration ephemeralSessionConfiguration]];
+	NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration ephemeralSessionConfiguration];
 	_cookies = [cookies copy];
 	_customPatterns = [customPatterns copy];
 
 	for (NSHTTPCookie *cookie in _cookies) {
-		[_session.configuration.HTTPCookieStorage setCookie:cookie];
+		[configuration.HTTPCookieStorage setCookie:cookie];
 	}
 
 	NSString *cookieValue = [NSString stringWithFormat:@"f1=50000000&f6=8&hl=%@", _languageIdentifier];
@@ -107,7 +107,9 @@ - (instancetype) initWithVideoIdentifier:(NSString *)videoIdentifier languageIde
 																		NSHTTPCookieSecure:@"TRUE"
 	}];
 
-	[_session.configuration.HTTPCookieStorage setCookie:additionalCookie];
+	[configuration.HTTPCookieStorage setCookie:additionalCookie];
+	configuration.HTTPAdditionalHeaders = @{@"User-Agent": @"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/12.0 Safari/605.1.15"};
+	_session = [NSURLSession sessionWithConfiguration:configuration];
 	_operationStartSemaphore = dispatch_semaphore_create(0);
 
 	return self;