Bug#987654: Adjusting severity

[Kunal Mehta]

severity 987654 serious
thanks

Upping priority to serious as this is technically a violation of policy 
that all software in main should be self-contained to main, and I 
believe there is a general acceptance in Debian that such privacy 
breaches are not acceptable (see also #726998).

I can also confirm that I finished testing the upstream patch and it 
worked as expected after running "sudo mailman-web collectstatic --clear 
&& sudo mailman-web compress".

-- Kunal