espree.parse mutates options argument

[not-an-aardvark]

Using espree 3.4.1:

const options = { ecmaFeatures: {} }

require('espree').parse('foo', options);

console.log(options.ecmaFeatures);

Expected behavior: options.ecmaFeatures should still be an empty object.

Actual behavior: options.ecmaFeatures is { impliedStrict: false }

This issue came up when I was looking into freezing the default config object for eslint.