package/janus-gateway: fix CVE-2021-4020

Fix CVE-2021-4020: janus-gateway is vulnerable to Improper
Neutralization of Input During Web Page Generation ('Cross-site
Scripting')

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>