Fixed syntax error in SQL fitler constants

inabox.database.sqlite/SQLiteProvider.cs

@@ -1411,7 +1411,7 @@ namespace InABox.Database.SQLite
                 FilterConstant.StartOfNextWeek => "datetime(date(), 'weekday 0', '+1 days')",
                 FilterConstant.EndOfNextWeek => "datetime(date(), 'weekday 0', '+8 days', '-000.0001 seconds')",
                 
-                FilterConstant.StartOfLastMonth => "datetime(date(), 'start of month', -1 month')",
+                FilterConstant.StartOfLastMonth => "datetime(date(), 'start of month', '-1 month')",
                 FilterConstant.EndOfLastMonth => "datetime(date(), 'start of month', '-000.0001 seconds')",
                 FilterConstant.StartOfThisMonth => "datetime(date(), 'start of month')",
                 FilterConstant.EndOfThisMonth => "datetime(date(), 'start of month', '+1 month', '-000.0001 seconds')",