Log message:
textproc/ruby-differ: add version 0.1.2

This is required by new version of textproc/ruby-kramdown-rfc2629.

Differ

Differ is a flexible, pure-Ruby diff library, suitable for use in both
command line scripts and web applications.  The flexibility comes from the
fact that diffs can be built at completely arbitrary levels of granularity
(some common ones are built-in), and can be output in a variety of formats.