Use an unversioned docdir.
--- doc/Makefile.am.orig	2009-07-13 18:55:00.000000000 -0500
+++ doc/Makefile.am	2020-08-31 15:56:37.000000000 -0500
@@ -2,7 +2,7 @@
 
 SUBDIRS = spec
 
-docdir = $(datadir)/doc/$(PACKAGE)-$(VERSION)
+docdir = $(datadir)/doc/$(PACKAGE)
 
 static_docs = vp3-format.txt color.html \
 	draft-ietf-avt-rtp-theora-00.xml \
--- doc/spec/Makefile.am.orig	2009-07-13 18:55:00.000000000 -0500
+++ doc/spec/Makefile.am	2020-08-31 15:56:37.000000000 -0500
@@ -3,7 +3,7 @@
 # makefile to generate the spec document from sources
 # requires transfig and pdflatex
 
-docdir = $(datadir)/doc/$(PACKAGE)-$(VERSION)
+docdir = $(datadir)/doc/$(PACKAGE)
 
 built_docs = Theora.pdf