Fix peerDependencies for npm@7 and typings

[tex0l]

Currently :

• we cannot use react-native-scrypt with npm@7 with other versions of react-native than "^0.41.2" because npm@7 fails if peerDependencies are not met ;
• the typings are incorrect (they were not updated with the last PR)

This PR does the following changes:

• the react-native peerDependency to "react-native": "*";
• the typings to update it with the encoding argument and include the 2 other signatures (with Buffer and string I/O);
• import @types/node as a dependency to import Buffer type (which seems to be the best practice for exposing typings);
• as a side effect, the package-lock.json was updated to use the lockfileVersion: 2 with npm@7, which now includes peerDependencies (hence its dramatic lengthening);
• update the yarn.lock of the example project;
• the CHANGELOG.

@ggozad tell me if you want me to change something in the way the outlined issues are solved :)

[ggozad]

Thanks :)

[tex0l]

You're welcome :), thank you for the quick merge :)