Explicitly set default encoding in createHash()
Explicitly set default encoding in createHash()

Up until now, the default encoding for this is `binary`, but
this is scheduled to change in Node 8. Since this module is
currently always passing string input to the `Hash` object,
it needs to account for that.

A better fix would likely involve dropping all strings handling
and treating binary data using Buffer objects, but I kept
this change minimal to avoid any breakage.

Refs: https://github.com/nodejs/node/pull/8611

malept/sumchecker,malept/sumchecker