fix for #1169: getPrototypeOf instead of __proto__

[gautaz]

📝 Description

This PR basically replaces __proto__ with Object.getPrototypeOf.

🎯 Relevant issues

This PR is related to issue #1169.

💎 Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

📜 Example code

NodeJS flag --disable-proto can now be used:

node --disable-proto=delete index.js

🚦 How Has This Been Tested?

The whole test plan is executed with --disable-proto=delete passed to NodeJS.

🏁 Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have commented my code, particularly in hard-to-understand areas

[gautaz]

I've just checked that the README sample can be run by deno with this fix applied.

[icebob]

Good job, thanks.