Version 2.1.1: libzip/zlib update and bug fixes

Version 2.1.1 fixes bugs:

• updates libzip to v1.7.3.1 and zlib to v 1.2.11.
• only marks the secure content extension as required if it is really required according to the specification.
• resolves a security issue (double free / use after free) in the usage of of libzip (https://talosintelligence.com/vulnerability_reports/TALOS-2020-1226)