Fix Process::MaybeShutdown's return type

src/process.cc

@@ -473,7 +473,7 @@ Process::Kill (int sig)
   return kill(pid_, sig);
 }
 
-int
+void
 Process::MaybeShutdown (void)
 {
   if (STDOUT_CLOSED && STDERR_CLOSED && got_chld_) {

src/process.h

@@ -36,7 +36,7 @@ class Process : EventEmitter {
   static void OnWritable (EV_P_ ev_io *watcher, int revents);
   static void OnCHLD (EV_P_ ev_child *watcher, int revents);
 
-  int MaybeShutdown (void);
+  void MaybeShutdown (void);
   void Shutdown (void);
 
   ev_io stdout_watcher_;