Fix 2.1 incompatibility related to `register` link

Hi, I noticed this when I enabled your theme. You were using a link that 404/not found. Just figured i would update it.

Add "Darkly" Bootswatch

* master:
  Bump version to 2.1.4

* master:
  Gulpfile adjustments
  Fixes #52: Fix table layout to avoid overflow
  Whitespace
  Flat badge!
  Overhaul Gulpfile
  Update GitHub release badge
  Add spinner to "more" pager when loading content
  Add spinner to comment editing form while loading
  Revert "Treat `.FormWrapper`s as form groups"
  Reset data list `list-style`
  Treat `.FormWrapper`s as form groups
  Revert "Adjust form spacing"
  Compile data list footer fix changes
  Fix data list footer styling
  Adjust form spacing
  Treat `.Gloss` in headings the same as `<small>`
  Implement page headers
  Adjust message list margins
  Fix whitespace trimming in Markdown files

This reverts commit bbe25e61.

This reverts commit 28567501.

* master:
  Don't hardcode component spacing
  Style `.CategoryBox`es as panels
  Style `.Alert`s as badges

* master:
  Bump version to 2.1.3
  Improve modal animations and backdrop structure
  Add icon for "Message" sprite
  Apply pagination link styling to first-level `div`s
  Add icon for "BestOf" sprite
  Add icon for "UnansweredQuestions" sprite
  Attach JS events on document ready
  Flesh out button group implementation
  Style data table wraps as panels
  Style category groups as panels
  Add styling for @mention autocomplete (At.js)
  Bump version to 2.1.2
  Fixes #47: Hide everything following the message form when editing comments
  Add icons for "Signatures" and "Quote" sprites
  Nuke margins on first and last elements in messages
  Add spinner to modal backdrop while dialog is loading
  Use `gulp-plumber` for catching errors