Fixed incorrect string for analytics parameter ScreenName (#71)

Author: albertb22

source/Firebase/Analytics/Extension.cs

@@ -82,7 +82,7 @@ public static class ParameterNamesConstants
 		public static NSString Quantity { get; } = new NSString ("quantity");
 		public static NSString Score { get; } = new NSString ("score");
 		public static NSString ScreenClass { get; } = new NSString ("screen_class");
-		public static NSString ScreenName { get; } = new NSString ("score_name");
+		public static NSString ScreenName { get; } = new NSString ("screen_name");
 		public static NSString SearchTerm { get; } = new NSString ("search_term");
 		public static NSString Shipping { get; } = new NSString ("shipping");
 		public static NSString Method { get; } = new NSString ("method");