Fixed build.

Makefile

@@ -17,6 +17,7 @@ test-doc:
 	# ignore warnings about missing subdirs - cloned from another repositories
 	mkdir ./doc/optional_modules/assets/ 2>/dev/null
 	mkdir ./doc/optional_modules/pricing/ 2>/dev/null
+	mkdir -p www/_build/html/ 2>/dev/null
 	echo "test\n=====" > ./doc/optional_modules/assets/index.rst
 	echo "test\n=====" > ./doc/optional_modules/pricing/index.rst
 	cd ./doc && make html