Fix bug in apps page
Fix bug in apps page

The `githubify_fragment_id` functionality moved to the
`DeveloperDocsRenderer` class in
https://github.com/alphagov/govuk-developer-docs/pull/101.

alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs