Fix Buffer deprecation warnings

[ob-stripe]

r? @remi-stripe @rattrayalex-stripe
cc @stripe/api-libraries

Using new Buffer is deprecated, cf. https://nodejs.org/api/buffer.html#buffer_new_buffer_array. This PR replaces uses of new Buffer with Buffer.alloc(size) or Buffer.from(string) as appropriate.

[remi-stripe]

this LGTM but deferring to @rattrayalex-stripe who is more familiar with node

[rattrayalex-stripe]

Sadly it seems that both Buffer.from and Buffer.alloc were added in Node v5.10.0. It seems we claim support for Node 4.

I'd be in favor of supporting Node 6+ and dropping support for Node 4 and Node 5, which would of course require a major version bump. We could also check whether Buffer.from is defined before using it, etc.

[ob-stripe]

@rattrayalex-stripe We use the safe-buffer package to backport those methods to early Node versions.

We should probably drop support for Node < 6 at some point, but we don't need to for this specific PR.

[rattrayalex-stripe]

Ah, terrific! Sorry I missed that.

LGTM

[ob-stripe]

No worries, thanks Alex!

[ob-stripe]

Released as 6.20.1.