doc: remove changelog.html from doc make target

not essential for doc build and currently broken because
tools/build_changelog.sh requires ./node.

leaving as separate make target so it can be invoked
separately in future.

PR-URL: https://github.com/iojs/io.js/pull/285
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

Makefile

@@ -189,7 +189,7 @@ website_files = \
 	out/doc/sh_main.js    \
 	out/doc/sh_javascript.min.js
 
-doc: $(apidoc_dirs) $(website_files) $(apiassets) $(apidocs) tools/doc/ out/doc/changelog.html $(NODE_EXE)
+doc: $(apidoc_dirs) $(website_files) $(apiassets) $(apidocs) tools/doc/ $(NODE_EXE)
 
 $(apidoc_dirs):
 	mkdir -p $@