Provided a name for MySql LAST_INSERT_ID call to allow the result to map correclty.

Dapper.Contrib/SqlMapperExtensions.cs

@@ -734,7 +734,7 @@ public int Insert(IDbConnection connection, IDbTransaction transaction, int? com
     {
         var cmd = String.Format("insert into {0} ({1}) values ({2})", tableName, columnList, parameterList);
         connection.Execute(cmd, entityToInsert, transaction, commandTimeout);
-        var r = connection.Query("Select LAST_INSERT_ID()", transaction: transaction, commandTimeout: commandTimeout);
+        var r = connection.Query("Select LAST_INSERT_ID() id", transaction: transaction, commandTimeout: commandTimeout);
 
         var id = r.First().id;
         if (id == null) return 0;
@@ -744,7 +744,7 @@ public int Insert(IDbConnection connection, IDbTransaction transaction, int? com
         var idp = propertyInfos.First();
         idp.SetValue(entityToInsert, Convert.ChangeType(id, idp.PropertyType), null);
 
-        return id;
+        return (int)id;
     }
 
     public void AppendColumnName(StringBuilder sb, string columnName)