update data source links

Author: drkane

findthatpostcode/templates/about.html.j2

@@ -26,20 +26,20 @@
   <h2 class="f2-ns f3 header-font normal" id="data-sources">Data sources</h2>
   <ul>
     <li><strong>Postcode data</strong>: <a class="link blue underline-hover"
-        href="https://geoportal.statistics.gov.uk/datasets/national-statistics-postcode-lookup-november-2019">NSPL</a>
+        href="https://geoportal.statistics.gov.uk/search?q=PRD_NSPL&sort=Date%20Created%7Ccreated%7Cdesc">NSPL</a>
     </li>
     <li><strong>Area data</strong>: <a class="link blue underline-hover"
-        href="https://geoportal.statistics.gov.uk/datasets/code-history-database-june-2019-for-the-united-kingdom">Code
+        href="https://geoportal.statistics.gov.uk/search?q=PRD_CHD&sort=Date%20Created%7Ccreated%7Cdesc">Code
         History Database</a> and
       <a class="link blue underline-hover"
-        href="https://geoportal.statistics.gov.uk/datasets/register-of-geographic-codes-june-2019-for-the-united-kingdom">Register
+        href="https://geoportal.statistics.gov.uk/search?q=PRD_RGC&sort=Date%20Created|created|desc">Register
         of Geographic Codes</a>
     </li>
     <li><strong>Boundary data</strong>: <a class="link blue underline-hover"
         href="http://geoportal.statistics.gov.uk/datasets?q=Latest_Boundaries&sort_by=name&sort_order=asc">ONS
         Geoportal</a></li>
     <li><strong>Placenames</strong>: <a class="link blue underline-hover"
-        href="https://geoportal.statistics.gov.uk/datasets/index-of-place-names-in-great-britain-september-2019">Index
+        href="https://geoportal.statistics.gov.uk/search?q=PRD_IPN&sort=Date%20Created|created|desc">Index
         of Place Names in Great Britain</a></li>
     <li><strong>MSOA names</strong>: <a class="link blue underline-hover"
         href="https://houseofcommonslibrary.github.io/msoanames/">House of Commons Library</a> (<a