fix type definition for package: apex.js

[y13i]

After #13796 has been merged, I noticed that it has an export default problem similar to this. It produces an error apex_js_1.default is not a function.

So I edited the definition and the test. Sorry for my poor checking before last PR.

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[dt-bot]

apex.js/index.d.ts

to author (@y13i). Could you review this PR?
👍 or 👎?

Checklist

• pass the Travis CI test?