Fix EXIT chunk being sent twice

nailgun-server/src/main/java/com/facebook/nailgun/NGCommunicator.java

@@ -338,7 +338,7 @@ void exit(int exitCode) {
 
     // send the command - client will exit
     try (PrintStream exit = new PrintStream(new NGOutputStream(this, NGConstants.CHUNKTYPE_EXIT))) {
-      exit.println(exitCode);
+      exit.print(exitCode);
     }
     isExited = true;
 

nailgun-server/src/test/java/com/facebook/nailgun/NGCommunicatorTest.java

@@ -18,6 +18,7 @@
 
 package com.facebook.nailgun;
 
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.mockito.Mockito.mock;
@@ -89,4 +90,15 @@ void canWriteData() throws IOException {
 
     verify(ostream).write(data, 0, data.length);
   }
+
+  @Test
+  void canSendExitCode() throws IOException {
+    ByteArrayOutputStream output = new ByteArrayOutputStream();
+    when(socket.getOutputStream()).thenReturn(output);
+
+    NGCommunicator comm = new NGCommunicator(socket, 0);
+    comm.exit(42);
+
+    assertArrayEquals(new byte[] {0x00, 0x00, 0x00, 0x02, 'X', '4', '2'}, output.toByteArray());
+  }
 }