Fix issue when pass 1 in .parsePhoneCode('1') method

[kasims07]

when you pass 1 in CountryParser.parsePhoneCode('1') that time multiple country have 1 as phone code so i do modification in below condition with singleWhere to fistWhere.

static Country _getFromPhoneCode(String phoneCode) {
return Country.from(
json: countryCodes.firstWhere(
(Map<String, dynamic> c) => c['e164_cc'] == phoneCode,
),
);
}