refactor: add correct types to input ref

[gabrielyotoo]

Fixes #279

[alexrabin]

Need this!

[gabrielyotoo]

@bhrott said he won't maintain this package anymore. If you would like to, you can still use my repo in your projects:

in package.json

"dependencies": {
-  "react-native-masked-text": "^1.13.0",
  "react-native-masked-text": "git+https://github.com/gabrielyotoo/react-native-masked-text",
}