Standard - 5.1.2.1 Ref to Message 3.2.3 is wrong

[Nat Sakimura]

Currently, it says:

{{{ Access Token Response documented in Sec 3.2.3 of OpenID Connect Messages 1.0 [OpenID.Messages]. }}}

It should point to Section 2.2.3.

[Nat Sakimura]

Fix #375 Standard - 5.1.2.1 Ref wrong

→ c016940e8d1c