Fix :doc completion candidates, they do not depend on the current word

Fixes #845

rc/core/doc.kak

@@ -30,7 +30,7 @@ def -hidden -params 1..2 _doc-open %{
 
 def -params 1..2 \
     -shell-candidates %{
-        find "${kak_runtime}/../doc/kak/manpages/" -type f -iname "*$@*.gz" -printf '%f\n' | while read l; do
+        find "${kak_runtime}/../doc/kak/manpages/" -type f -iname "*.gz" -printf '%f\n' | while read l; do
             printf %s\\n "${l%.*}"
         done
     } \