roman: use stringBuild for better performance(?)

roman/roman.go

@@ -1,11 +1,13 @@
 package roman
 
+import "strings"
+
 func ConvertToRoman(arabic int) string {
-	var converted string
+	var converted strings.Builder
 	if arabic <= 3 {
 		for i := 0; i < arabic; i++ {
-			converted += "I"
+			converted.WriteString("I")
 		}
 	}
-	return converted
+	return converted.String()
 }