Add missing rm -rf ebin back to docs task

Author: José Valim

Makefile

@@ -101,6 +101,7 @@ docs: compile ../ex_doc/bin/ex_doc
 	rm -rf docs
 	cp -R -f lib/*/ebin/*.beam ./ebin
 	bin/elixir ../ex_doc/bin/ex_doc "Elixir" "$(VERSION)" -m Kernel -u "https://github.com/elixir-lang/elixir" --source-ref "$(call SOURCE_REF)"
+	rm -rf ebin
 
 ../ex_doc/bin/ex_doc:
 	@ echo "ex_doc is not found in ../ex_doc as expected. See README for more information."