[iOS] fix handling kerning, wordSpacing and letterSpacing when Number
[iOS] fix handling kerning, wordSpacing and letterSpacing when Number

https://github.com/react-native-community/react-native-svg/issues/568#issuecomment-485518338

react-native-community/react-native-svg,magicismight/react-native-svg,magicismight/react-native-svg,magicismight/react-native-svg,react-native-community/react-native-svg,magicismight/react-native-art-svg,react-native-community/react-native-svg,react-native-community/react-native-svg,magicismight/react-native-art-svg,magicismight/react-native-svg,magicismight/react-native-svg,react-native-community/react-native-svg