Fix process.platform

src/node.cc

@@ -1684,7 +1684,7 @@ static void Load(int argc, char *argv[]) {
 
 
   // process.platform
-  process->Set(String::NewSymbol("platform"), String::New("PLATFORM"));
+  process->Set(String::NewSymbol("platform"), String::New(PLATFORM));
 
   // process.argv
   Local<Array> arguments = Array::New(argc - option_end_index + 1);