Update jwt.go

jwt/jwt.go

diff --git a/jwt/jwt.go b/jwt/jwt.go
index e747bd9..52570f3 100644
--- a/jwt/jwt.go
+++ b/jwt/jwt.go
@@ -60,7 +60,7 @@
 		return ErrInvalidSUBClaim
 	}
 	if iat, ok := v.Expected.IssuedAt(); ok {
-		if t, ok := j.Claims().GetTime("iat"); t != iat && ok {
+		if t, ok := j.Claims().GetTime("iat"); t != iat || !ok {
 			return ErrInvalidIATClaim
 		}
 	}