DOC: internals: Fix spelling errors in filters.txt

(cherry picked from commit d80f5c0d0cd9133fada06bff71f98a025366c7c8)
Signed-off-by: Willy Tarreau <w@1wt.eu>
(cherry picked from commit 88b65f4d6b709eafa83537c44e486513c8ec45f5)
Signed-off-by: Willy Tarreau <w@1wt.eu>
1 file changed