showCountryCodePickerBottomSheet has background color set to transparent

[david-legend]

showCountryCodePickerBottomSheet has background color set to transparent.
Please expose background color in widget api for it to be possible for users to change it.

[MrRoy121]

Transparent support added in #75

CountryCodePicker(
  backgroundColor: Colors.transparent,
  dialogBackgroundColor: Colors.transparent,
  boxShadow: [],
)

Thank you for the suggestion..