www/element-web: Update to 1.8.4

MFH: 2021Q3
Approved by: maintainer (implicit, version bump, as per PR 258262)
Security: 93eb0e48-14ba-11ec-875e-901b0e9408dc
Security: CVE-2021-40823
Security: CVE-2021-40824

(cherry picked from commit bfecb22ee6c3675fc306ab9e2e3652e4f1423b9e)