Move Python 3.7 to *security* mode on downloads page (#1607)

Author: ned-deily

templates/downloads/index.html

@@ -60,7 +60,7 @@ <h2 class="widget-title">Active Python Releases</h2>
                         </li>
                         <li>
                             <span class="release-version">3.7</span>
-                            <span class="release-status">bugfix</span>
+                            <span class="release-status">security</span>
                             <span class="release-start">2018-06-27</span>
                             <span class="release-end">2023-06-27</span>
                             <span class="release-pep"><a href="https://www.python.org/dev/peps/pep-0537">PEP 537</a></span>