Fallback to globalThis in acorn.js if this is not available

[yorinasub17]

This increases compatibility of the included acorn.js file to support environments that don't support a root this object (e.g., Deno) by falling back to globalThis if this is not defined.

When using the base JS-Interpreter with Deno, the following error happens:

error: TypeError: Cannot read properties of undefined (reading 'acorn')
  mod(root.acorn || (root.acorn = {})); // Plain browser env
           ^
    at https://raw.githubusercontent.com/NeilFraser/JS-Interpreter/10a8cf5e613834b5d36655c1921f818455fc324a/acorn.js:32:12
    at https://raw.githubusercontent.com/NeilFraser/JS-Interpreter/10a8cf5e613834b5d36655c1921f818455fc324a/acorn.js:33:3

This patch resolves the error.