Update upgradingFromPreviousVersionsOfGrails.gdoc
GRAILS-10432: RESTful url mappings documentation should use includes/excludes
fix unintended strikethrough in commandLine forkedMode documentation

In the section heading for "Debugging and Forked Execution (--debug vs --debug-fork)",
the double-hyphens before the --debug and --debug-fork were not being rendered correctly,
and debug was being rendered as a strikethrough.  This change appears to result in the
intended rendering.