fix save and also add proper format to the default options similar to …

[apolloid]

…that of default option

Hi KoalaBear,
Great Jobs for the first draft in this functionality which I need but upon trying to implement your code, I found that there are some issues where the owner might reject it, mainly:

1. The defaultOption implemented by original owner is in the form of {key:any, value:any}, however, the current implementation for for defaultOptions is in the form of ['valueA', 'valueB'].
2. It does not work with the save functionality. It will setselected to value instead of key even if I have set it to save='key'.

For above issues, I had corrected them and updated an example in README:
import { MultipleSelectList } from 'react-native-dropdown-select-list'

const App = () => {

  const [selected, setSelected] = React.useState([]);
  
  const data = [
    {key:'1',value:'Jammu & Kashmir'},
    {key:'2',value:'Gujrat'},
    {key:'3',value:'Maharashtra'},
    {key:'4',value:'Goa'},
  ]

  return(
    <MultipleSelectList 
      onSelect={() => alert(selected)}
      setSelected={(val) => setSelected(val)} 
      data={data} 
      save="key"
      defaultOptions={[ {key:'1', value:'Jammu & Kashmir' }, {key:'4', value:'Goa' }]}   //default selected options
    />
  )

};

[apolloid]

while using the package, found one more issue,
initialize defaultOptions=[]
as without this those people who never declare props defaultOptions will have error