Bugfix: Make find a class method instead of an instance method

When we call the standard `ActiveRecord.find` it's on the class, not the
instance so `Persistable` needs to reflect that fact.

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Change-Id:     I78d2c478429dde615b154a5e38dacf6b96d5ef46
Signed-off-by: Jeff Felchner <accounts+git@thekompanee.com>
Version Bump to 1.8.1