Add missing period to uvm document history item

Author: emlun

index.bs

@@ -9999,7 +9999,7 @@ The following changes were made to the [=Web Authentication API=] and the way it
 Changes:
 
 - Updated timeout guidance: [[#sctn-timeout-recommended-range]]
-- `uvm` extension no longer included; see instead L2 [[webauthn-2-20210408]]
+- `uvm` extension no longer included; see instead L2 [[webauthn-2-20210408]].
 - [=authData/attestedCredentialData/aaguid=] in [=attested credential data=] is no longer zeroed
     when {{PublicKeyCredentialCreationOptions/attestation}} preference is {{AttestationConveyancePreference/none}}: [[#sctn-createCredential]]