Allow installation with lunr 0.8 (#880)

Lunr has released version 0.8.0.  It is still compatible with lunr.js
version 2.3.9 that is bundled in this project.

https://github.com/yeraydiazdiaz/lunr.py/blob/0.8.0/lunr/__init__.py#L6

Author: carlwgeorge

setup.cfg

@@ -42,7 +42,7 @@ install_requires =
     requests
     attrs
     docutils>=0.17
-    lunr>=0.6.2,<0.8.0
+    lunr>=0.6.2,<0.9.0
     configargparse
 
     toml; python_version < "3.11"