Dropped support for Node <16

[TLeszczynskiWA]

Hey,
I've noticed that the newest version (1.4.1) doesn't work on pre-16 Node versions. That's the error:

TypeError [ERR_INVALID_ARG_TYPE]: The "key" argument must be of type string or an instance of Buffer, TypedArray, DataView, or KeyObject. Received an instance of ArrayBuffer
    at new NodeError (internal/errors.js:322:7)
    at prepareSecretKey (internal/crypto/keys.js:322:11)
    at new Hmac (internal/crypto/hash.js:111:9)
    at Object.createHmac (crypto.js:146:10)
    at zCe (/var/task/index.js:104:39810)
    at Object.Vlt [as createLMv2Response] (/var/task/index.js:104:39953)
    at Object.Klt (/var/task/index.js:104:43424)
    at /var/task/index.js:104:48437
    at p (/var/task/index.js:104:47086)
    at Object.next (/var/task/index.js:104:46369)

I've decided to dig a little and I think I know why it happens now. Basically, js-md4 buffer method (which has been deprecated btw) that is used to create a hash used as a key for HMAC returns an ArrayBuffer. The thing is - ArrayBuffer support in crypto's createHmac has been added in Node v16.

Create a hash and pass it to createLMv2Response
Util used for hash generation - uses js-md4 buffer that returns ArrayBuffer
MD4 hash passed down
The ArrayBuffer hash being passed to crypto.createHmac and breaking pre-16 Node versions