fix a protobuf bug

Aircraft.proto

@@ -14,6 +14,6 @@ message Aircraft {
     string     type        = 3; // aircraft ICAO type
     string     wtc         = 4; // WTC
     string     wakeRecat   = 5; // wake recatogization category
-    Int32      engineCount = 6; // number of engines
+    int32      engineCount = 6; // number of engines
     EngineType engineType  = 7; // engine type
 }