Obsolete approach to tracing

[henk84]

rbot/bin/rbot

Line 72 in 6070ef6

set_trace_func proc { |event, file, line, id, binding, classname|

https://docs.ruby-lang.org/en/master/Kernel.html#method-i-set_trace_func says:

Note: this method is obsolete, please use TracePoint instead.