Fix danger changelog path

This should fix broken MRs that had changelogs:

/usr/local/bundle/gems/danger-5.6.4/lib/danger/danger_core/plugins/dangerfile_gitlab_plugin.rb:197:in `block in html_link':  (Danger::DSLError)
[!] Invalid `Dangerfile` file: 
[!] Invalid `Dangerfile` file: undefined method `start_with?' for #<Pathname:scripts/support/changelog/Dangerfile>
 #  from scripts/support/changelog/Dangerfile:32
 #  -------------------------------------------
 #    # YAML could not be parsed, fail the build.
 >    fail "#{gitlab.html_link(path)} isn't valid YAML! #{SEE_DOC}"
 #  end