fix output_encoding of #decipher

`#decipher` had the order of `output_encoding` and `input_encoding` swapped, which is correct, but forgot to call `#final` using `input_encoding` rather than `output_encoding`.

This pull request fixes that, and provides two tests to verify that basic usage of `#cipher` and `#decipher` work (as well as a command to validate style using `npm run lint`).