GUACAMOLE-1834: Merge required '%s' for extlinks configuration.

diff --git a/src/conf.py b/src/conf.py
index b83bb5d..a536c5e 100644
--- a/src/conf.py
+++ b/src/conf.py
@@ -47,7 +47,7 @@
 
 # Allow shorthand notation for JIRA issue links
 extlinks = {
-    'jira': ( 'https://issues.apache.org/jira/browse/%s', '')
+    'jira': ( 'https://issues.apache.org/jira/browse/%s', '%s')
 }
 
 templates_path = [ '_templates' ]