#3085 sp_BlitzIndex Output Param

Oops! Almost missed the last minute addition from @paulneering. Closes #3085.

Author: BrentOzar

sp_BlitzIndex.sql

@@ -1714,7 +1714,7 @@ BEGIN TRY
             they could see performance slowdowns - see Github #3085. */
             DECLARE @MissingIndexPlans BIGINT;
             SET @StringToExecute = N'SELECT @MissingIndexPlans = COUNT(*) FROM ' + QUOTENAME(@DatabaseName) + N'.sys.dm_db_missing_index_group_stats_query;'
-            EXEC sp_executesql @StringToExecute, N'@MissingIndexPlans BIGINT OUT', @MissingIndexPlans;
+            EXEC sp_executesql @StringToExecute, N'@MissingIndexPlans BIGINT OUT', @MissingIndexPlans OUT;
 
             IF @MissingIndexPlans > 1000
                 BEGIN