Update ruby-kramdown to 0.13.7.

kramdown 0.13.7 released

This release, aside from fixing bugs and some other minor changes, adds a new
converter for removing HTML tags from an element tree. This means that one can
now do

kramdown -i html -o remove_html_tags,kramdown my_document.html

and get a nice kramdown document from a full HTML document!

Changes

1 major change

  * Implemented RemoveHtmlTags converter for removing HTML tags from an
    element tree (fixes bug RF#29282 requested by Bernard Potocki)

3 minor changes

  * Updated kramdown binary to support multiple, chained output formats

  * Added a new option for setting a default coderay highlighting language
    (requested by Lou Quillio)

  * Feature request RF#29575: Added support for ­ soft-hyphen entity
    (requested by Alexander Groß)

5 bug fixes

  * Fixed bug RF#29576: Footnotes in headers resulted in duplicated id attr in
    TOC (reported by korthaerd)
  * Multi-line titles in links are now correctly parsed
  * DOCTYPE declaration is now correctly parsed independent of case
  * Setting of nil options works now by using the String ‘nil’
  * Fixed table-of-content test cases (test went green although the meaning of
    the test was not satisfied due to copy-paste - d’oh!)

1 documentation fix

  * Fixed bug RF#29577: sidebar link to news page was broken for HTML pages in
    sub directories (reported by korthaerd)

(taca)