Support React 17

[binarykitchen]

Almost everyone is on React 17 these days but not this library:

npm ERR! Could not resolve dependency:
npm ERR! peer react@"^16.0.0" from react-password-strength@2.4.0
npm ERR! node_modules/react-password-strength
npm ERR!   react-password-strength@"2.4.0" from the root project

Reasons this isn't happening?