Fix for lib0 issue 88: Expired JWT error

[AIRoboCoder]

Fix for issue: https://github.com/dmonad/lib0/issues/88 which also fixes issue https://github.com/yjs/y-redis/issues/25

Changes:

• Added getUnixTimeInSeconds() to time.js: returns time since unix epoch in seconds
• Fix for verifyJWT in crypto/jwt.js: compare exp with value from timegetUnixTimeInSeconds as per RFC7519