Not all fileds are passed down from DecimalNumberPicker to NumberPicker

[Menasi Ephrem]

Hey,

First of all awesome library thank you for making it 👍. One minor fix, some of the DecimalNumberPicker fields are not passed down to the NumberPicker making it hard to customize the look and feel of DecimalNumberPicker.

NumberPicker/lib/src/decimal_numberpicker.dart

Line 30 in ba1da0c

 this.itemCount = 3,