Diff footer ajax navigation doesn't load diffs

[jmcarp]

Steps:

• Open a diff page, e.g. https://atf-eregs-demo.apps.cloud.gov/diff/447-1/2014-18842/2015-12992?from_version=2014-18842
• Click the "next" footer nav link

Expected:

• Browser fetches the diff view for the next section
• Url changes to the url for the next diff section

Actual:

• Browser fetch the reg section view for the next section
• Url changes to the url for the next next reg section

Fix coming in a minute.