(Re)initialize $formatted_dates.

[adam-vessey]

Avoid accumulating multiple values.

GitHub Issue: Fixes #95

• Other Relevant Links (Google Groups discussion, related pull requests,
  Release pull requests, etc.)

What does this Pull Request do?

A brief description of what the intended result of the PR will be and/or what
problem it solves.

What's new?

A in-depth description of the changes made by this PR. Technical details and
possible side effects.

• Changes x feature to such that y
• Added x
• Removed y
• Does this change require documentation to be updated?
• Does this change add any new dependencies?
• Does this change require any other modifications to be made to the repository
  (i.e. Regeneration activity, etc.)?
• Could this change impact execution of existing code?

How should this be tested?

A description of what steps someone could take to:

• Reproduce the problem you are fixing (if applicable)
• Test that the Pull Request does what is intended.
• Please be as detailed as possible.
• Good testing instructions help get your PR completed faster.

Additional Notes:

Any additional information that you think would be helpful when reviewing this
PR.

Interested parties

Tag (@ mention) interested parties or, if unsure, @Islandora/committers