changelog: Make Zulip 4.8 - 4.11 headings consistent.

docs/overview/changelog.md

@@ -329,7 +329,7 @@ log][commit-log] for an up-to-date list of raw changes.
 
 ## Zulip 4.x series
 
-## Zulip 4.11 -- 2022-03-15
+### 4.11 -- 2022-03-15
 
 - CVE-2022-24751: Zulip Server 4.0 and above were susceptible to a
   race condition during user deactivation, where a simultaneous access
@@ -342,7 +342,7 @@ log][commit-log] for an up-to-date list of raw changes.
   - The server is upgraded, which clears the cache.
 - Updated translations.
 
-## Zulip 4.10 -- 2022-02-25
+### 4.10 -- 2022-02-25
 
 - CVE-2022-21706: Reusable invitation links could be improperly used
   for other organizations.
@@ -359,7 +359,7 @@ log][commit-log] for an up-to-date list of raw changes.
 - Fix ARM64 support; however, the wal-g binary is not yet supported on
   ARM64 (zulip/zulip#21070).
 
-## Zulip 4.9 -- 2022-01-24
+### 4.9 -- 2022-01-24
 
 - CVE-2021-43799: Remote execution of code involving RabbitMQ.
 - Closed access to RabbitMQ port 25672; initial installs tried to
@@ -397,7 +397,7 @@ log][commit-log] for an up-to-date list of raw changes.
   `upgrade-zulip-from-git` require 3 GB of RAM, or 2 GB and at least 1
   GB of swap.
 
-## Zulip 4.8 -- 2021-12-01
+### 4.8 -- 2021-12-01
 
 - CVE-2021-43791: Zulip could fail to enforce expiration dates
   on confirmation keys, allowing users to potentially use expired