Adding Symbol() as a field's value

[n14little]

Describe the bug
Adding a Symbol() as a field's value panics with parsing failed: ParseIntError { kind: InvalidDigit }

To Reproduce
Add the following to tests/js/test.js

// tests/js/test.js
const obj = {
  x: 1,
  y: Symbol(),
  z: 3
};

and then run:

$ cargo run -- ./tests/js/test.js

Expected behavior
I would expect that the code successfully parse and not panic.

Build environment (please complete the following information):

• OS: Ubuntu Linux
• Version: 18.04
• Target triple: x86_64-unknown-linux-gnu
• Rustc version: rustc 1.43.1 (8d69840ab 2020-05-04)

Additional context
Add any other context about the problem here.

[n14little]

Just put up a PR for this. The issue was fixed somewhere and the code in the PR just re-instates the ignored tests and then adds the branch for checking if a value is a symbol.