version bump + allow not setting iat/nbf/exp in builder

[Mythra]

fixes #37

Motivation (required)

In the refactor adding in the time crate, the token builder silently required that the fields:

• nbf (not before)
• iat (Issued at)
• exp (expired)

Had to all be set in order to be valid. Creating too strict of a validation sequence. It should only validate attributes that are present.

Test Plan (required)

• Tests should pass (there is a new test added not adding any of these fields).