Question: minimum supported Ruby version

[tagliala]

Hello,

is there a minimum supported Ruby version?

According to the test matrix, it would be 2.6, but specs pass against 2.5, and 2.4.

In order to make them pass against 2.3,

They do not pass on 2.2 because kramdown should be < 2, and even after

     Psych::DisallowedClass:
       Tried to load unspecified class: Thread::Mutex

Can we set the minimum required Ruby version to 2.3, or even newer?

Reason: #1085