feat(18): displaying + for positive month comparison

wrapping + into span inline, to make it behave like part of
surrounding text in a div, somewhat ok

18-expenses-chart/main.go

@@ -20,7 +20,7 @@ func main() {
 			Balance:                    500 + rand.Float32()*1000,
 			Expenses:                   []float32{randomDailyExpense(), randomDailyExpense(), randomDailyExpense(), randomDailyExpense(), randomDailyExpense(), randomDailyExpense(), randomDailyExpense()},
 			TotalThisMonth:             50 + rand.Float32()*600,
-			PercentComparedToLastMonth: 5 * rand.Float32(),
+			PercentComparedToLastMonth: -5 + 10*rand.Float32(),
 		})
 		component.Render(context.Background(), w)
 	})