doc: correct crypto encoding information

Checklist

• make -j4 test (UNIX), or vcbuild test nosign (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

doc

Description of change

The default encoding for crypto methods was changed in v6.0.0, with v4.x keeping a default of binary.

Ref: https://github.com/nodejs/node/commit/b010c8716498dca398e61c388859fea92296feb3