jwt: fix bad test message style
jwt: fix bad test message style

Change-Id: I84c311778a1ad3e824e65c1e797223f51f0bc2ea
Reviewed-on: https://go-review.googlesource.com/27890
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/oauth2