Adjust date and deadline

The actual candidate recommendation happened on a different date.
Update them to match the actual date of publication.

Author: Raymond Toy

index.bs

@@ -4,8 +4,8 @@ Shortname: webaudio
 Level: 1
 Group: audiowg
 Status: CR
-Date: 2020-12-15
-Deadline: 2020-01-15
+Date: 2021-01-14
+Deadline: 2021-02-15
 Prepare for TR: yes
 ED: https://webaudio.github.io/web-audio-api/
 TR: https://www.w3.org/TR/webaudio/