axe.getFrameContexts mutates its input

[WilcoFiers]

This shouldn't fail:

const context = { exclude: [['iframe', 'foo']] }
axe.utils.getFrameContexts(context);
assert.deepEqual(context, { exclude: [['iframe', 'foo']] });

[padmavemulapati]

Validated with the latest develop branch code base,
on passing the axe.utils.getFrameContexts({exclude: [['iframe','#testFrame']] });
for a test file
"http://qateam.dequecloud.com/attest/api/test.html" , and id of the iframe being #testFrame
and it excluding the frame contexts, below is the screenshot,

[straker]

No docs