[MDC103] Swift Step4 wrong theme

[Luecy1]

in "Change the typeface of the login screen" section codelab page

wrong

MDCButtonTypographyThemer.applyTypographyScheme(typographyScheme, to: cancelButton)

fix

MDCTextButtonColorThemer.applySemanticColorScheme(colorScheme, to: self.cancelButton)

when i apply wrong code,cancel button theme is the same as next button.