modified MagicNumberChecker to avoid warnings when val token starts with upper case

Scala recommend when defining constant, use upper case on first letter.
but, current MagicNumberChecker does not allow "val" definition like below,

    val NewYearsEve = (12, 31)

because current MagicNumberChecker only allow simple "val" definition (like only contains single integer literal)

I updated MagicNumberChecker to allow "val" definition when its contains upper case on first letter.