Update PaymentServer.

https://github.com/PrivateStorageio/PaymentServer/pull/101

Before:

$ ci-tools/count-vulnerabilities <security-report.json
Vulnerable packages: 94
Vulnerability count: 250

After:

$ ci-tools/count-vulnerabilities <security-report.json
Vulnerable packages: 84
Vulnerability count: 257

The vulnerabilities went up because of a bug in the current version of vulnix we are use (https://whetstone.privatestorage.io/privatestorage/PrivateStorageio/-/issues/93#note_16389). In this case, the derivation of binutils used by PaymentServer, which had a number of fixes for CVEs applied was masking the version used by python-2.7 (both of which had the same version number).