src: fix whitespace/indent cpplint warnings

PR-URL: https://github.com/nodejs/node/pull/7462
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

src/node_watchdog.h

@@ -48,6 +48,7 @@ class SigintWatchdog {
   v8::Isolate* isolate() { return isolate_; }
   bool HasReceivedSignal() { return received_signal_; }
   void HandleSigint();
+
  private:
   void Destroy();