tools: make eslint work on subdirectories

The old pattern didn't include files in lib/internal. This changes the
pattern to directories which makes eslint apply to all subdirectories as
well.

PR-URL: #1686
Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>

Makefile

@@ -375,7 +375,7 @@ bench-idle:
 	./$(NODE_EXE) benchmark/idle_clients.js &
 
 jslint:
-	./$(NODE_EXE) tools/eslint/bin/eslint.js src/*.js lib/*.js --reset --quiet
+	./$(NODE_EXE) tools/eslint/bin/eslint.js src lib --reset --quiet
 
 CPPLINT_EXCLUDE ?=
 CPPLINT_EXCLUDE += src/node_lttng.cc