clear text field in case of invalid input

journalmarks/templates/index.html

@@ -34,7 +34,7 @@ function run() {
          } else if(url.match(/^[a-z0-9]{4}$/)) {
              window.location.href = '/' + url;
          } else {
-             console.log('not a URL and not a tag');
+             document.getElementById('url').value = '';
          }
     });