Deprecation Warning use new Buffer() → Buffer.from()

[dersimn]

When using for e.g. spotifyApi.refreshAccessToken(); (which uses new Buffer()):

(node:79216) [DEP0005] DeprecationWarning: Buffer() is deprecated due to security and usability issues. Please use the Buffer.alloc(), Buffer.allocUnsafe(), or Buffer.from() methods instead.
(Use `node --trace-deprecation ...` to show where the warning was created)

From what I found here this will however drop support for Node.js ≤ 5.9.x.

[coveralls]

Coverage remained the same at 97.866% when pulling fac8c68cf279bbb56567183f59eec93c6066c19b on dersimn:pr/2 into be15f1c742b35134ce5bd35521d8bf1ab1ba67cf on thelinmichael:master.