Spawn factorio server deteached in client.js

Sending ^C via the terminal on Linux may cause SIGINT to be sent twice
to the factorio process, causing it to exit without completing the
saving.  This happens because the shell sends the interupt to all
members of the process group for the job and this includes both the
node client process and the factorio server process.

Avoid this situation by passing detached to spawn when the platform is
Linux, which causes the process to be created with its own process group
and therefore not targeted by a SIGINT from the shell.

This unfortunately does not work on Windows as we can't send SIGINT or
^C to a process there.  Doing subprocces.kill on Windows terminates the
process similarly to how SIGKILL works on Linux.

CHANGELOG.md

@@ -6,7 +6,10 @@ Version 1.2.1
 
 - Updated node-factorio-api to v0.3.8 to fix mod downloads randomly breaking
   ([#229][#229].)
+- Fixed SIGINT being sent twice to Factorio server when interrupted by CTRL+C
+  on Linux ([#217][#217].)
 
+[#217]: https://github.com/clusterio/factorioClusterio/issues/217
 [#229]: https://github.com/clusterio/factorioClusterio/issues/229
 
 ### Breaking Changes

client.js

@@ -359,7 +359,8 @@ write-data=${ path.resolve(config.instanceDirectory, instance) }\r\n
             '--rcon-port', Number(process.env.RCONPORT) || instconf.clientPort,
             '--rcon-password', instconf.clientPassword,
         ], {
-            'stdio': ['pipe', 'pipe', 'pipe']
+			'stdio': ['pipe', 'pipe', 'pipe'],
+			'detached': process.platform === "linux",
         }
     );
     factorio.stdout.on("data", data => {
@@ -471,7 +472,8 @@ write-data=${ path.resolve(config.instanceDirectory, instance) }\r\n
 				'--server-settings', instancedirectory + '/server-settings.json',
 				'--port', args.port || Number(process.env.FACTORIOPORT) || instanceconfig.factorioPort
 			], {
-				'stdio': ['pipe', 'pipe', 'pipe']
+				'stdio': ['pipe', 'pipe', 'pipe'],
+				'detached': process.platform === "linux",
 			}
 		);