rec: Fix the version of alabaster when building the doc

Fixes
```
The alabaster extension used by this project needs at least Sphinx v3.4; it therefore cannot be built with this version.
```

diff --git a/pdns/recursordist/docs/requirements.txt b/pdns/recursordist/docs/requirements.txt
index 85b4511975f006117350068b662fa0e5b490b1fe..08f7ee915349059431201d5b5db46eb5ee008ddf 100644 (file)
--- a/pdns/recursordist/docs/requirements.txt
+++ b/pdns/recursordist/docs/requirements.txt
@@ -7,3 +7,4 @@ sphinxcontrib.httpdomain
 sphinxcontrib-fulltoc
 docutils!=0.15,<0.18
 jinja2<3.1.0
+alabaster==0.7.13