chore(bip-0046): fix date format in Post-History header

Author: theborakompanioni

bip-0046.mediawiki

@@ -8,7 +8,7 @@
   Type: Standards Track
   Created: 2022-04-01
   License: CC0-1.0
-  Post-History: 2022-5-1: https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-May/020389.html
+  Post-History: 2022-05-01: https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-May/020389.html
 </pre>
 
 == Abstract ==