[client-app] Upgrade `is-online` package - fix online detection behind proxy
[client-app] Upgrade `is-online` package - fix online detection behind proxy

Summary:
Thus upgrade includes https://github.com/sindresorhus/is-online/pull/39
which should fix the offline notification status issues we are seeing in
T8174 for people running Nylas behind a firewall or proxy

Test Plan: manual

Reviewers: mark, halla, evan

Reviewed By: evan

Differential Revision: https://phab.nylas.com/D4455

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