A new version of PyJWT==2.0.0 got released a few days back which
changes a few significant things such as return types and option
names, see:
03610f0103/CHANGELOG.md (v200)
This commit edits the code of refstack in order to comply with the newest
changes of PyJWT.
Change-Id: I153384cd39ebadb8ee9eb3d99cd21aa02b8c0673