Update to latest govspeak gem

Specifically, this resolves an issue with rendering multiple footnote
references.
Filter statistics announcements by organisation

The statistics announcements page in admin now defaults to showing the
current user's organisation's announcements. The filter allows other
organisations to be selected, as well as all organisations.
Include acronym in organisation select
Merge pull request #1646 from alphagov/fix-footnotes-bug

Update to latest govspeak gem
Merge pull request #1647 from alphagov/filter-announcements-by-org

Filter statistics announcements by organisation