Compatible with github.com/dgrijalva/jwt-go v3.1.0
Fix #1: Update to github.com/dgrijalva/jwt-go v3.1.0 https://github.com/dgrijalva/jwt-go/issues/221
Fix #1: Update to github.com/dgrijalva/jwt-go v3.1.0 https://github.com/dgrijalva/jwt-go/issues/221