Revert "Use `Buffer.from` in place of `new Buffer`"
Revert "Use `Buffer.from` in place of `new Buffer`"

This reverts commit e930afdcf79aee9dc596785dfe75af74c8f438e2.

Many Node users are not on Node 6 yet.

rabbitmq/rabbitmq-website,rabbitmq/rabbitmq-website,rabbitmq/rabbitmq-website,rabbitmq/rabbitmq-website,rabbitmq/rabbitmq-website