CVE 2021 25943 fix2

[wid]

Hi,

The CVE-2021-25943 security is now 1 year old and raises npm audit issues.

So, I applied the following recommandation:

#159 (comment)

with units tests into this pull request.

Nothing else has been changed. The npm test is still 100%:
`

[email protected] test
lab -c -l -t 100 -a code
..................................................
..................................................
..................................................
...............
165 tests complete
Test duration: 58 ms
Assertions count: 608 (verbosity: 3.68)
Coverage: 100.00%
Can you please accept this PR and publish an npm package accordingly ?

Note that I changed the implementation after review with my team, I silently ignore set with forbidden keys like in https://github.com/tjmehta/keypather/pull/43/files instead of throwing an error.
Test have been updated accordingly.

[tjmehta]

other people have reported this we do not consider prototype pollution a security issue for 101. for example, lodash set is similar and does not handle prototype pollution.

developers that use any user passed strings with set or file is the real security issue. this is not IMO.

happy to look at anything if you see something, thanks!