Added changelog for version 1.8.0. [skip ci]

Author: jlesage

appdefs.xml

@@ -109,6 +109,11 @@ Where:
     </documentation>
     <!-- Changelog of the application. -->
     <history>
+      <release>
+        <version>1.8.0</version>
+        <date>2020-04-15</date>
+        <change>Upgraded Nginx Proxy Manager to version 2.2.3.</change>
+      </release>
       <release>
         <version>1.7.4</version>
         <date>2020-04-08</date>