GUACAMOLE-773: Remove use of XHTML-style self-closing tags from normal HTML.

This is particularly important for AngularJS 1.8.x and jQuery 3.5.0+,
which will no longer correct this automatically with their HTML
prefilters, resulting in unexpected nesting of tags when the browser
interprets something like "<div/>" as "<div>" (older versions of jQuery
would have corrected "<div/>" to "<div></div>").

See:

 * https://docs.angularjs.org/guide/migration#migrating-from-1-7-to-1-8
 * https://jquery.com/upgrade-guide/3.5/

extensions/guacamole-auth-totp/src/main/resources/templates/authenticationCodeField.html

@@ -41,7 +41,7 @@
     <div class="totp-code">
         <input type="text"
                placeholder="{{'TOTP.FIELD_PLACEHOLDER_CODE' |translate}}"
-               ng-model="model" autocorrect="off" autocapitalize="off"/>
+               ng-model="model" autocorrect="off" autocapitalize="off">
     </div>
 
 </div>