Bug#930636: python3-service-identity: new version available (for quite a time now)

[Peter Gervai]

Package: python3-service-identity
Version: 16.0.0-2
Severity: normal

v18.1.0 is available since last year. Also seems to package nicely using the 
16.0 
debian dir, so possibly a no-brainer. But please, since matrix-synapse needs it.

thanks!