Update to 1.12.0.2

changelog:
pandoc (1.12.0.2)

  * Removed `stringable` dependency.

pandoc (1.12.0.1)

  * Allow `--metadata` to be repeated for the same key to form a list.
    This also has the effect that `--bibliography` can be repeated,
    as before.

  * Handle boolean values in `--metadata`.  Note that anything not parseable
    as a YAML boolean or string is treated as a literal string.
    You can get a string value with "yes", or any of the strings interpretable
    as booleans, by quoting it:

        -M boolvalue=yes -M stringvalue='"yes"'

  * LaTeX writer: Don't print references if `--natbib` or `--biblatex`
    option used.

  * DOCX writer: Add `settings.xml` to the zip container.  Fixes a bug
    in which docx files could not be read by some versions of Word
    and LibreOffice (#990).

  * Fixed a regression involving slide shows with bibliographies.
    The Div container around references messed up the procedure for carving
    a document into slides.  So we now remove the surrounding Div in
    `prepSlides`.

  * More informative error message when a filter is not found in path.

  * Depend on pandoc-types 1.12.1.  This provide `ToJSONFilter`
    instances for `Data a => a -> [a]` and `Data a => a -> IO [a]`.

  * Don't use unicode_collation in building OSX package:
    it adds something like 50MB of dependencies to the package.

  * Declare alex and happy as build-tools (#986).