[#753] Fix: api.helper.get.is_delegated_inbox function

[moodsey211]

changing the html selector to check for the svg element instead of the html class

https://github.com/KartikTalwar/gmail.js/issues/753

[josteink]

Hey there and thanks for the patch!

I can't test this feature myself, but the change itself looks innocent enough.

If you bump the version-number and update the changelog, I'll merge and get a new release out on npmjs.