doc/_ext: accomodate three active releases in the Ceph timeline

Avoid this error:
```
/home/jenkins-build/build/workspace/ceph-pr-docs/doc/releases/index.rst:64: ERROR: Error in "ceph_timeline" directive:
maximum 3 argument(s) allowed, 4 supplied.
```

Signed-off-by: Laura Flores <lflores@ibm.com>

diff --git a/doc/_ext/ceph_releases.py b/doc/_ext/ceph_releases.py
index 94e92ffdd6acdc99d636c7fbda06634de8529e7e..481c2a1b6194414538def5552ca18c1ea27dfb3b 100644 (file)
--- a/doc/_ext/ceph_releases.py
+++ b/doc/_ext/ceph_releases.py
@@ -191,7 +191,7 @@ class ReleasesGantt(Directive):
 
 class CephTimeline(Directive):
     has_content = False
-    required_arguments = 3
+    required_arguments = 4
     optional_arguments = 0
     option_spec = {}