Switch from dgrijalva/jwt-go to form3tech-oss/jwt-go.

dgrijalva/jwt-go has been abandoned and contains several serious
security issues. Most projects are now switching to the form3tech fork.

See https://snyk.io/vuln/SNYK-GOLANG-GITHUBCOMDGRIJALVAJWTGO-596515 for
info on the issues.

Signed-off-by: Dan Lorenc <dlorenc@google.com>

server/auth/jwt.go

@@ -21,7 +21,7 @@ import (
 	"errors"
 	"time"
 
-	jwt "github.com/dgrijalva/jwt-go"
+	jwt "github.com/form3tech-oss/jwt-go"
 	"go.uber.org/zap"
 )
 

server/auth/options.go

@@ -21,7 +21,7 @@ import (
 	"io/ioutil"
 	"time"
 
-	jwt "github.com/dgrijalva/jwt-go"
+	jwt "github.com/form3tech-oss/jwt-go"
 )
 
 const (