[oauth/errors] Properly coerce unicode strings.
[oauth/errors] Properly coerce unicode strings.

Summary: Fixes T440

Test Plan: regression

Reviewers: emfree

Reviewed By: emfree

Maniphest Tasks: T440

Differential Revision: https://review.inboxapp.com/D464

ErinCall/sync-engine,closeio/nylas,closeio/nylas,ErinCall/sync-engine,wakermahmud/sync-engine,EthanBlackburn/sync-engine,wakermahmud/sync-engine,closeio/nylas,gale320/sync-engine,ErinCall/sync-engine,gale320/sync-engine,Eagles2F/sync-engine,wakermahmud/sync-engine,jobscore/sync-engine,PriviPK/privipk-sync-engine,ErinCall/sync-engine,wakermahmud/sync-engine,EthanBlackburn/sync-engine,PriviPK/privipk-sync-engine,jobscore/sync-engine,Eagles2F/sync-engine,wakermahmud/sync-engine,nylas/sync-engine,Eagles2F/sync-engine,Eagles2F/sync-engine,nylas/sync-engine,gale320/sync-engine,PriviPK/privipk-sync-engine,gale320/sync-engine,ErinCall/sync-engine,closeio/nylas,gale320/sync-engine,EthanBlackburn/sync-engine,PriviPK/privipk-sync-engine,nylas/sync-engine,jobscore/sync-engine,EthanBlackburn/sync-engine,EthanBlackburn/sync-engine,nylas/sync-engine,jobscore/sync-engine,PriviPK/privipk-sync-engine,Eagles2F/sync-engine