feat(versions): add new 4B versions

feat(revisions): Rpi 4B v1.2

fix(revision match): fix overclock revision match

Merge pull request #13 from RatherSlowTurtle/fix/overclock-revision-match

fix(revision match): fix overclock revision match

fix(build): remove node 6 support

fix(README): get it to publish a new version

readme.md: Fix syntax error in the example

Fix the following error in the example provide in section Usage:

let rpi = require('raspi-ver);
                  ^^^^^^^^^^^^

SyntaxError: Invalid or unexpected token

Signed-off-by: Leon Anavi <[email protected]>